Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario: December 13, 2020 to May 19, 2024

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 1

SURVEILLANCE REPORT

Adverse Events Following Immunization (AEFIs)

for COVID-19 in Ontario: December 13, 2020 to

May 19, 2024

This report provides a summary of adverse events following immunization (AEFIs) that are temporally

associated (i.e., occur after receiving the vaccine) with receipt of COVID-19 vaccine and meet the

provincial surveillance definitions (i.e., confirmed).

It is important to note that AEFIs described in this

report are defined as any untoward medical occurrences that followed immunization and do not

necessarily have a causal relationship with the vaccine.

This summary includes AEFIs reported in the Public Health Case and Contact Management Solution

(CCM) as of May 19, 2024 and doses administered up to and including May 19, 2024 in the Ontario

Ministry of Health’s COVaxON

application (see technical notes for details on data sources). Data were

extracted on May 21, 2024.

Background

In Ontario, AEFIs are reported to local public health units (PHUs) by health care providers and vaccine

recipients.

PHUs investigate and assess all AEFI reports, which are then entered into the provincial

electronic reporting system according to provincial surveillance guidelines.

Please see the following

resources for more information:

 Public Health Ontario’s (PHO) overview of vaccine safety surveillance for more information on

vaccine safety surveillance in Ontario

 The technical annex of PHO’s annual vaccine safety report for technical details on vaccine safety

surveillance data analysis in Ontario

 The government of Canada’s COVID-19 vaccine safety webpage for national data on COVID-19

vaccine safety

 PHO’s COVID-19 vaccine webpage for resources and data on Ontario’s COVID-19 vaccine

program

Note: PHO is moving towards reporting our COVID-19 AEFIs on an annual basis, which is aligned

with other (non-COVID-19) AEFI reporting. This is the final monthly AEFI for COVID-19

surveillance report. Reporting will occur annually moving forward.

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 2

Highlights

There are a total of 23,415 AEFI reports received following 40,493,562 doses of COVID-19 vaccines

administered in Ontario to date with a reporting rate of 57.8 per 100,000 doses administered (0.06 %

of all doses administered). This represents an increase of 57 new AEFI reports compared to the

previous report.

Of the total 23,415 AEFI reports received to date:

 22,129 AEFI reports are non-serious (94.5% of total AEFI reports)

 1,286 AEFI reports meet the serious definition (5.5% of total AEFI reports)

 The most commonly reported adverse events are ‘other severe or unusual events’ and ‘allergic

skin reactions’, reported in 28.2% and 22.5% of the total AEFI reports, respectively

 1,774 reports include a COVID-19 vaccine-specific adverse event of special interest, in which

772 reports also meet the serious definition (see Adverse events of special interest section for

more information)

To date, two safety signals have been confirmed for COVID-19 vaccines based on AEFIs reported in

Canada during the COVID-19 vaccination program roll-out: Thrombosis with thrombocytopenia

syndrome (TTS) and myocarditis/pericarditis. These two signals were also detected internationally. Refer

to the Adverse Event section of this report for more information.

Scientific data indicate that COVID-19 vaccines are safe and effective; the benefits of COVID-19 vaccines

continue to outweigh the risk of the disease. Ontario continues to monitor all AEFIs reported following

receipt of COVID-19 immunization in collaboration with its partners.

In Ontario, AEFIs that meet the serious definition are events that required hospital admission

and reports of death. Please see the technical notes for a full definition of serious AEFIs.

Several adverse events have been identified as COVID-19 vaccine-specific adverse events of

special interest (AESIs). The list of COVID-19 specific AESIs are listed in the technical notes.

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 3

Summary of AEFI Reports in Ontario

An AEFI report refers to a report received by the PHU, which pertains to one individual vaccine recipient who reported at least one adverse

event after receiving the COVID-19 vaccine (i.e., temporally associated with the vaccine). COVID-19 vaccines may be administered concomitantly

with, or at any time before or after non-COVID-19 vaccines including live, non-live, adjuvanted, or unadjuvanted vaccines for people 6 months of

age or older.

See Table 1 for a summary of all AEFI reports received to date in Ontario.

Table 1. Summary of AEFI reports by COVID-19 vaccine product: Ontario, December 13, 2020 to May 19, 2024

Pfizer-

BioNTech

Comirnaty

Pfizer-

BioNTech

Comirnaty

Bivalent

BA.4/5

Pfizer-

BioNTech

Comirnaty

XBB.1.5

Moderna

Spikevax

Moderna

Spikevax

Bivalent

BA.1

Moderna

Spikevax

Bivalent

BA.4/5

Moderna

Spikevax

XBB.1.5

AstraZeneca

Vaxzevria/

COVISHIELD

Janssen

Jcovden

(Johnson

Johnson)

Novavax

Nuvaxovid

All vaccine

products

combined

Total number of

AEFI reports

13,722

225

100

7,307

198

1,701

23,415

Number of non-

serious reports

13,017

207

6,908

186

1,568

22,129

Number of

serious reports

705

399

133

1,286

Proportion of total

AEFI reports that

are serious (%)

5.1

8.0

7.0

5.5

6.1

4.5

13.4

7.8

0.0 0.0

5.5

Doses

administered

23,619,626

2,317,334

1,720,330

9,634,538

1,256,504

140,947

692,439

1,087,759

4,006

16,677

40,493,562

Total reporting

rate per

100,000 doses

administered

58.1

9.7

5.8

75.8

15.8

15.6

11.8

156.4

499.3

221.9

57.8

Serious reporting

rate per

100,000 doses

administered

3.0

0.8

0.4

4.1

1.0

0.7

1.6

12.2

0.0

3.2

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 4

Notes:

 The columns above for Pfizer-BioNTech Comirnaty and Moderna Spikevax COVID-19 vaccines include AEFIs associated with all indicated dosages: 3 mcg, 10

mcg and 30 mcg for Pfizer-BioNTech Comirnaty and 25 mcg, 50 mcg and 100 mcg for Moderna Spikevax. Moderna Spikevax Bivalent BA.1 (50 mcg), Moderna

Spikevax Bivalent BA.4/5 (50 mcg) and Pfizer-BioNTech Comirnaty Bivalent BA.4/5 (10 mcg and 30 mcg) COVID-19 vaccines are presented separately and

were previously recommended vaccine products before the approval of the XBB.1.5-containing COVID-19 mRNA vaccines. Currently, Pfizer-BioNTech

Comirnaty XBB.1.5 and Moderna Spikevax XBB.1.5 COVID-19 vaccines are approved and recommended for vaccinating individuals who were not previously

vaccinated and as additional doses for those previously vaccinated in approved age groups.

 Novavax Nuvaxovid includes Novavax Nuvaxovid and Novavax Nuvaxovid XBB.1.5 Omicron subvariant COVID-19 vaccines.

 One AEFI report did not specify a vaccine product received.

 Reporting rate for the Janssen Jcovden (Johnson & Johnson) and Novavax Nuvaxovid COVID-19 vaccines should be interpreted with caution due to unstable

reporting rate arising from the relatively small number of doses administered.

Data Source: CCM, COVaxON

(see technical notes for details on data sources)

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 5

Table 2. Number of AEFI reports and reporting rates by age group and sex: Ontario,

December 13, 2020 to May 19, 2024

Number of AEFI reports

received to date

Reporting rate per 100,000

doses administered

Sex: Female

17,168

81.1

Sex: Male

6,054

31.5

Ages: 0-4 years

44.7

Ages: 5-11 years

340

25.1

Ages: 12-17 years

827

39.2

Ages: 18-24 years

1,455

46.7

Ages: 25-29 years

1,440

57.0

Ages: 30-39 years

3,763

73.7

Ages: 40-49 years

4,546

92.1

Ages: 50-59 years

4,461

74.5

Ages: 60-69 years

3,549

52.2

Ages: 70-79 years

1,981

37.5

Ages: 80 years and over

986

31.7

Note:

 Age represents age at time of immunization. Gender is used when sex is missing. Some AEFI reports and doses

administered records have unknown sex, gender or age; these reports are excluded from sex and age-specific

counts and reporting rates.

Data Source: CCM, COVaxON

(see technical notes for details on data sources)

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 6

Figure 1. Number of AEFI reports and doses administered by week of vaccine administration: Ontario, December 13, 2020 to

May 19, 2024

Note:

 AEFI reports are assessed based on date of vaccine administration. The administration week ranges from week 51 (Dec 13 – 19, 2020) to week 20 (May 12

– 18, 2024). May 19, 2024 is not included in the figure as it is not yet a full week.

 The number of AEFI reports for the recent reporting weeks are subject to reporting delays and/or delayed data entry (i.e., reports are likely to still be under

investigation and yet to be reported as a confirmed AEFI report).

Data Source: CCM, COVaxON

(see technical notes for details on data sources)

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 7

Adverse Event Descriptions

For all COVID-19 vaccine products combined, the most commonly reported adverse events are

‘other severe or unusual events’ and ‘allergic skin reactions’, reported in 28.2% and 22.5% of the total

AEFI reports, respectively. Figure 2 shows the ten most frequently reported adverse events for all

COVID-19 vaccines combined.

To date, two safety signals have been confirmed for COVID-19 vaccines based on AEFIs reported in

Canada during the COVID-19 vaccination program roll-out: Thrombosis with thrombocytopenia

syndrome (TTS) and myocarditis/pericarditis. These two signals were also detected internationally.

Ontario continues to monitor all AEFIs reported following receipt of COVID-19 immunization in

collaboration with its partners.

Figure 2. Ten most frequently reported adverse events for all COVID-19 vaccines: Ontario,

December 13, 2020 to May 19, 2024

Note: An AEFI report may contain multiple adverse events. Thus the sum of all adverse event-specific counts will

not equal to the total number of AEFI reports.

Data Source: CCM

The ‘other severe or unusual events’ category includes reports of adverse events that do not meet any

other pre-defined events outlined in the Infectious Diseases Protocol: Appendix 1 but are assessed to be

clinically important or epidemiologically interesting.

These events usually require medical attention but

do not necessarily meet either the medically important event definition or the serious AEFI definition.

Serious AEFIs are described in the Serious AEFI section. The number of AEFI reports and reporting rate

for each adverse event are presented in Appendix A.

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 8

Medically Important Events

Some selected adverse events are defined as “medically important,” based on the World Health

Organization’s (WHO) guidance, regardless of whether they meet the serious AEFI definition. These types

of events may jeopardize the patient or may require intervention to prevent an outcome described in the

serious definition. The full list of medically important events are listed in the technical notes.

There were 704 reports with medically important events, representing 3.0% of all reports. The most

frequently reported medically important event was events managed as anaphylaxis (n=522), of which 40

met the definition of a serious AEFI (7.7%). See this resource for more information on management of

anaphylaxis following immunization in the community.

Adverse events of special interest (AESIs) for COVID-19 vaccines

Several adverse events of special interest (AESIs) for COVID-19 vaccines have been identified by

international health authorities based on a theoretical rationale for a possible association with COVID-19

vaccines. Reporting of AESIs for COVID-19 vaccines enables enhanced monitoring of events which may

otherwise not be captured in a passive surveillance system.

There were 1,774 reports with COVID-19 vaccine-specific AESIs, representing 7.6% of all reports. Of the

1,774 reports, 772 met the definition of a serious AEFI. The number of AEFI reports and reporting rate

for each AESI by vaccine product are presented in Appendix A.

MYOCARDITIS/PERICARDITIS

Rare myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the lining around

the heart) events have been reported following vaccination with COVID-19 mRNA vaccines.

Information

from vaccine safety monitoring systems and evidence from multiple observational studies across many

countries support an association between COVID-19 mRNA vaccines and an increased risk of

myocarditis/pericarditis.

10-12

Information to date indicates that these events occur more commonly after

the second dose, within the week following vaccination (typically within 4-5 days), mainly in

adolescents/young adults 12 to 29 years of age, and more often in males than females.

Vaccine safety surveillance data in Canada suggest relatively higher rates of myocarditis/pericarditis

reported after the original monovalent Moderna Spikevax COVID-19 vaccine compared to the original

monovalent Pfizer-BioNTech Comirnaty COVID-19 vaccine.

Similar trends have been observed in

Ontario’s vaccine safety surveillance data where the reporting rates of myocarditis/pericarditis was

observed to be higher following vaccination with the original monovalent Moderna Spikevax COVID-19

vaccine compared to the original monovalent Pfizer-BioNTech Comirnaty COVID-19 vaccine in the 18 to

24 year old age group, particularly among males.

There are no available data on the risk of

myocarditis/pericarditis following the currently recommended COVID-19 mRNA vaccine formulations

(i.e., Moderna Spikevax XBB.1.5, Pfizer-BioNTech Comirnaty XBB.1.5). Ontario’s COVID-19 vaccine

guidance provides more detailed information on vaccine recommendations and eligibility by age and

vaccine product, as well as additional information on myocarditis/pericarditis following vaccination with

a COVID-19 mRNA vaccine.

As of May 19, 2024, there have been 841 reports of myocarditis/pericarditis following receipt of COVID-

19 vaccines in Ontario, with 830 following mRNA vaccines. All reports of myocarditis/pericarditis are

assessed using the Brighton Collaboration case definition for myocarditis and the Brighton Collaboration

case definition for pericarditis. Ontario continues to monitor these events in collaboration with its

partners and updates can be found within this report and on the PHAC website.

For more information

on this topic, see the Canadian Immunization Guide on COVID-19 vaccines.

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 9

THROMBOSIS WITH THROMBOCYTOPENIA SYNDROME (TTS)

Thrombosis with thrombocytopenia syndrome (TTS) is a serious health condition characterized by the

presence of acute venous or arterial thrombosis (blood clot) with new onset thrombocytopenia (low

levels of platelets), and no known recent exposure to heparin. TTS emerged in 2021 as a new adverse

event following immunization with COVID-19 adenoviral vector-based vaccines, including AstraZeneca

Vaxzevria/COVISHIELD and Janssen Jcovden COVID-19 vaccines.

Vaccine-Induced Immune

Thrombotic Thrombocytopenia (VITT) refers to the clinical syndrome of TTS, in addition to laboratory

tests that confirm platelet activation (i.e., anti-platelet 4 antibodies). The province announced a pause

on the administration of first doses of the AstraZeneca Vaxzevria COVID-19 vaccine on May 11, 2021,

due to an observed increase in reports of TTS/VITT in Ontario. Health Canada cancelled the Drug

Identification Number (DIN) for Janssen Jcovden and AstraZeneca Vaxzevria COVID-19 vaccines in July

2023 and December 2023 respectively, at the request of the manufacturer pursuant of the Food and

Drug Regulations.

There have been 21 reports of TTS following the AstraZeneca Vaxzevria/COVISHIELD COVID-19 vaccine

in Ontario (including one probable TTS), with the most recent event having a vaccination date of May 6,

2021. All events were following the first dose of AstraZeneca Vaxzevria/COVISHIELD COVID-19 vaccine.

Based on the total number of AstraZeneca Vaxzevria/COVISHIELD COVID-19 vaccines administered in

Ontario to date, the reporting rate of TTS based on 21 reports is 1.9 per 100,000 doses administered

(approximately 1 in 51,800). The reporting rate of VITT (as a subtype of TTS) based on 16 reports is 1.5

per 100,000 doses administered (approximately 1 in 68,000). Of the 21 reports, 16 are confirmed as VITT

with positive anti-PF4 antibody test results. The remaining five TTS events that are not classified as VITT

have had VITT ruled out through testing (n=4) or did not have confirmatory tests ordered (n=1). There

has been one report of death recorded in CCM in an individual with VITT. A Coroner’s investigation

determined that the immediate causes of death included Vaccine-induced Immune Thrombotic

Thrombocytopenia (VITT). See Appendix A for the number of TTS/VITT reports by vaccine product.

As part of vaccine safety surveillance at the national level, the Advisory Committee on Causality

Assessment (ACCA) has conducted a review of reports of TTS following COVID-19 vaccines.

ACCA is a

committee of experts who review reports of AEFIs to determine whether an event was likely to have

been causally related to a given vaccine. ACCA reviewed 103 potential TTS reports following receipt of

any COVID-19 vaccine from across Canada. Among these reports, 37 were found to be “consistent with

causal association to immunization” using the World Health Organization’s (WHO) causality assessment

classification, including 16 from Ontario.

All 16 events followed administration of a viral vector vaccine

and all occurred between March and May 2021. A national summary of the ACCA assessment results is

published online.

Serious AEFIs

In Ontario, AEFIs that meet the serious definition are events that required hospital admission and

reports of death (see the technical notes for a full definition).

There were 1,286 AEFI reports classified as serious, representing 5.5% of all AEFI reports and a serious

AEFI reporting rate of 3.2 per 100,000 doses administered for all COVID-19 vaccine products combined.

Of the 1,286 reports meeting the serious definition, 1,241 reports had a hospital admission related to

the adverse event and 45 were reports of deaths. See Table 1 for serious AEFI reporting rate by vaccine

product. As a comparison, the proportion of AEFIs defined as serious for all vaccines administered in

Ontario ranged from 2.8% to 5.0% between 2012 and 2018.

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 10

AEFI REPORTS REQUIRING HOSPITALIZATION

Of the 1,241 reports of hospitalization, 488 were recovered at the time of reporting, 548 were not yet

recovered when the investigation was completed but likely to recover, and 106 reported persistent or

significant disability/incapacity related to the adverse event at the time of reporting. Due to the

relatively short follow-up time for AEFIs reported in CCM, it is uncertain whether these

disability/incapacity will eventually resolve, but had not yet resolved at the time of reporting. The

remaining reports had unknown outcome at the time of reporting.

AEFI REPORTS WITH FATAL OUTCOME

In Ontario, reports of death that meet the provincial AEFI surveillance case definition are those that are

temporally associated with vaccination, where no other clear cause of death can be established. Similar

to other events, reports of deaths are thoroughly investigated by the local PHU through the collection of

relevant information including a cause of death (e.g., autopsy or Coroner’s report). It is important to

note that these reports should not be interpreted as causally related with receipt of a vaccine.

As of May 19, 2024, there are 45 reports of death temporally associated with receipt of COVID-19

vaccine that met the provincial surveillance case definition. There was one death where AEFI may have

been a contributing factor of death; in this death, a Coroner’s investigation determined that the

immediate causes of death included VITT.

PHO continues to conduct continuous monitoring of the safety of COVID-19 vaccines in collaboration

with its partners, including individual case review of all serious AEFIs and daily analysis of surveillance

data for vaccine safety signals.

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 11

Geography

Table 3. Number of AEFI reports and reporting rates by public health unit and region: Ontario,

December 13, 2020 to May 19, 2024

Public Health Unit Name

Number of AEFI

reports received

to date

Reporting rate per

100,000 doses

administered

Northwestern Health Unit

203

90.9

Thunder Bay District Health Unit

159

35.4

TOTAL NORTH WEST

362

53.8

Algoma Public Health

172

51.2

North Bay Parry Sound District Health Unit

208

57.2

Porcupine Health Unit

149

69.5

Public Health Sudbury & Districts

457

80.6

Timiskaming Health Unit

108

120.8

TOTAL NORTH EAST

1,094

69.7

Eastern Ontario Health Unit

612

103.9

Hastings Prince Edward Public Health

230

47.9

Kingston, Frontenac and Lennox & Addington Public Health

492

74.1

Leeds, Grenville & Lanark District Health Unit

420

72.6

Ottawa Public Health

2,482

77.4

Renfrew County and District Health Unit

293

102.0

TOTAL EASTERN

4,529

78.0

Durham Region Health Department

3,308

172.5

Haliburton, Kawartha, Pine Ridge District Health Unit

571

102.3

Peel Public Health

1,500

40.4

Peterborough Public Health

306

70.9

Simcoe Muskoka District Health Unit

864

53.0

York Region Public Health

1,868

58.4

TOTAL CENTRAL EAST

8,417

73.5

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 12

Public Health Unit Name

Number of AEFI

reports received

to date

Reporting rate per

100,000 doses

administered

Toronto Public Health

2,703

33.5

TOTAL TORONTO

2,703

33.5

Chatham-Kent Public Health

29.2

Grey Bruce Health Unit

200

42.0

Huron Perth Public Health

426

100.8

Lambton Public Health

612

174.6

Middlesex-London Health Unit

357

25.0

Southwestern Public Health

482

84.3

Windsor-Essex County Health Unit

398

36.7

TOTAL SOUTH WEST

2,557

55.4

Brant County Health Unit

170

43.5

City of Hamilton Public Health Services

665

43.4

Haldimand-Norfolk Health Unit

22.7

Halton Region Public Health

957

55.7

Niagara Region Public Health

568

43.1

Region of Waterloo Public Health and Emergency Services

805

50.3

Wellington-Dufferin-Guelph Public Health

519

59.6

TOTAL CENTRAL WEST

3,753

48.5

TOTAL ONTARIO

23,415

57.8

Note: Orientation of AEFI reports by geography is based the case's public health unit of residence at the time of the

adverse event. This does not represent the location of vaccine administration. Reporting rates should not be

interpreted as incidence rates. In the context of a passive AEFI surveillance system, a higher overall reporting rate of

AEFIs does not necessarily suggest a vaccine safety concern; rather, it is an indicator of a robust passive vaccine safety

surveillance system. Reporting rates are valuable estimates for comparing to other passive surveillance systems and

for monitoring reporting trends over time.

Data Source: CCM, COVaxON (see technical notes for details on data sources)

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 13

Technical Notes

Data Sources

The data for this report were based on:

 AEFI information from the Public Health Case and Contact Management Solution (CCM)

extracted on May 21, 2024 at approximately 8:30 a.m.

 Doses administered data from the Ontario Ministry of Health’s COVaxON application extracted

on May 21, 2024 at approximately 7:00 a.m.

Data Caveats

 Data presented in this report only represent AEFIs reported to public health units and

recorded in CCM. As a result, all counts will be subject to varying degrees of reporting bias,

including underreporting, particularly for mild or common reportable events, as well as

stimulated (elevated) reporting, which can occur in response to media coverage and increased

public awareness.

 CCM and COVaxON are dynamic reporting systems which allow ongoing updates to data

previous entered. As a result, data extracted from CCM and COVaxON represent a snapshot at

the time of data extraction and may differ from previous or subsequent reports.

 Data corrections or updates can result in AEFI reports being removed and/or updated from past

reports and may result in counts differing from past publicly reported AEFIs.

Methods

 For provincial surveillance reporting, an adverse event must occur after receiving the vaccine

and meet the MOH AEFI case definition.

Data presented in this report only includes AEFI

reports with a confirmed case classification and an association with a COVID-19 vaccine in CCM

at the time of data extraction.

 AEFI reports from CCM where the Disposition was reported as ENTERED IN ERROR, DOES NOT

MEET DEFINITION or DUPLICATE – DO NOT USE, or any variation on these values have been

excluded. AEFI reports from CCM where the Status was reported as MERGED-OBSOLETE have

also been excluded.

 AEFI reports with a missing date of vaccine administration have been excluded. If an AEFI report

has more than one vaccination entered (i.e., it was unclear if the adverse event was attributed

to the first or the second dose of the series), then the administration date of the first dose was

used for the analysis.

 Each AEFI report refers to an individual who reported an adverse event after receiving a dose of

COVID-19 vaccine. An AEFI report may contain multiple adverse events. Therefore, the total

number of adverse events can exceed the number of individual AEFI reports reported in a given

time frame. AEFI reports that did not have an adverse event reported at the time of data

extraction have been excluded.

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 14

 AEFI reporting rates are calculated using the number of COVID-19 vaccine-specific AEFIs

reported in a given time period in Ontario divided by doses of COVID-19 vaccines administered

in the same time period in Ontario. AEFIs that are reported in Ontario following vaccines that

were administered outside of Canada with a Health Canada-approved vaccine are included in

the calculation of reporting rates. The number of such reports are small and has minimal impact

on the reporting rates.

 Male/Female information presented in this report are sourced from the Sex field in CCM and are

intended to represent sex assigned at birth. The doses administered data from the COVaxON

application are presented by gender, which is used as a proxy for doses administered by sex in

calculating sex-specific reporting rates.

 Serious AEFIs are defined using the World Health Organization (WHO) standard definition:

AEFI that results in death, is life-threatening, requires in-patient hospitalization or prolongs an

existing hospitalization, results in persistent or significant disability/incapacity, or in a congenital

anomaly/birth defect. Due to data limitations and the relatively brief follow-up period of AEFIs

reported in Ontario, AEFI reports that meet the serious definition typically have an in-patient

hospitalization or death reported. In-patient hospitalization is defined as having a hospital

admission recorded in CCM. Deaths are defined as reporting ‘fatal’ in the outcome field in CCM.

 Some selected adverse events can be defined as “medically important,” based on the World

Health Organization’s (WHO) guidance, regardless of whether they meet the serious AEFI

definition. These types of events may jeopardize the patient or may require intervention to

prevent an outcome described in the serious definition (e.g., hospitalization); “medically

important” events may be defined after applying medical and scientific judgement. In Ontario,

the specific events under surveillance that align with this definition include: acute disseminated

encephalomyelitis (ADEM), events managed as anaphylaxis, encephalitis/encephalopathy,

Guillain-Barré syndrome (GBS), intussusception, meningitis, myelitis/transverse myelitis

and thrombocytopenia.

 All reports of events managed as anaphylaxis, GBS, myocarditis, pericarditis and TTS/VITT are

further assessed using the internationally recognized case definition from the Brighton

Collaboration. An independent review of these cases is completed and a preliminary score is

assigned based on this case definition. This score is not a measure of severity but rather reflects

the level of diagnostic certainty, with level 1 being the most highly specific for the condition.

 Several adverse events of special interest (AESI) following administration of COVID-19 vaccine(s)

were selected for surveillance.

These are: vaccine-associated enhanced disease, multisystem

inflammatory syndrome in children and adults, acute respiratory distress syndrome, acute

cardiovascular injury, myocarditis/pericarditis, coagulation disorder (including thrombotic

events), thrombosis with thrombocytopenia syndrome (TTS) and vaccine-induced immune

thrombotic thrombocytopenia (VITT), acute kidney injury, acute liver injury, anosmia and/or

ageusia, chilblain-like lesions, single organ cutaneous vasculitis, erythema multiforme, acute

pancreatitis, rhabdomyolysis, and subacute thyroiditis.

 Orientation of case counts by geography is based on the Permanent Health Unit in CCM.

Permanent Health Unit refers to the case's public health unit of residence at the time of adverse

event. Cases for which the Permanent Health Unit was reported as MOH-PHO (to signify a case

that is not a resident of Ontario) have been excluded from the analyses.

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 15

References

1. Ontario. Ministry of Health. Infectious diseases protocol: appendix 1: provincial case definitions for

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immunization.pdf?la=en

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immunization-guide-part-4-active-vaccines/page-26-covid-19-vaccine.html#a10.2

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pericarditis.html

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thrombocytopenia syndrome (TTS) [Internet]. Decatur, GA: Task Force for Global Health; 2021 [cited

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syndrome-interim-case-definition/

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health/services/immunization/vaccine-safety/advisory-committee-causality-assessment.html

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user manual for the revised WHO classification second edition, 2019 update. Geneva, CH: World

Health Organization; 2019. [cited 2023 Sep 25]. Available from:

https://iris.who.int/bitstream/handle/10665/340802/9789241516990-eng.pdf?sequence=1

18. Public Health Agency of Canada; National Advisory Committee on Immunization. Thrombosis with

thrombocytopenia syndrome: findings from the advisory committee on causality assessment

[Internet]. Ottawa, ON: Government of Canada; 2023 [cited 2023 Sep 25]. Available from:

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committee-causality-assessment/thrombosis-thrombocytopenia-syndrome-findings.html

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vaccine safety in Ontario, 2018 [Internet]. Toronto, ON: Queen’s Printer for Ontario; 2019 [cited

2021 Jan 26]. Available from: https://www.publichealthontario.ca/-

/media/documents/a/2019/annual-vaccine-safety-report-2018.pdf?la=en

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definitions and standards for expedited reporting E2A [Internet]. Version 4. Geneva: ICH; 1994 [cited

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Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 17

21. Ontario Agency for Health Protection and Promotion (Public Health Ontario). Adverse events of

special interest (AESIs) for COVID-19 vaccines surveillance. Toronto, ON: Queen's Printer for Ontario;

2020 [cited 2021 Jul 19]. Available from: https://www.publichealthontario.ca/-

/media/documents/ncov/vaccines/2020/12/covid-19-guidance-aesis.pdf?la=en

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 18

Appendix A

Table A1. Number of AEFI reports by adverse event and COVID-19 vaccine product: Ontario, December 13, 2020 to May 19, 2024

Adverse event

Pfizer-

BioNTech

Comirnaty

Pfizer-

BioNTech

Comirnaty

Bivalent

BA.4/5

Pfizer-

BioNTech

Comirnaty

XBB.1.5

Moderna

Spikevax

Moderna

Spikevax

Bivalent

BA.1

Moderna

Spikevax

Bivalent

BA.4/5

Moderna

Spikevax

XBB.1.5

AstraZeneca

Vaxzevria/

COVISHIELD

Janssen

Jcovden

(Johnson

Johnson)

Novavax

Nuvaxovid

All vaccine

products

combined

Other severe or

unusual events*

4,205

1,758

463

6,611

Allergic skin

reactions

3,385

1,477

281

5,262

Pain/redness/

swelling at the

injection site

1,582

2,108

325

4,147

Rash

1,371

874

189

2,512

Anaesthesia/

paraesthesia

1,211

397

215

1,874

Adenopathy/

lymphadenopathy

868

364

1,312

Arthritis/ arthralgia

711

252

107

1,116

Fever in

conjunction with

another reportable

event

478

384

171

1,062

Severe vomiting/

diarrhea

560

303

149

1,037

AESI - Myocarditis/

pericarditis

523

295

841

Event managed as

anaphylaxis†

369

122

522

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 19

Adverse event

Pfizer-

BioNTech

Comirnaty

Pfizer-

BioNTech

Comirnaty

Bivalent

BA.4/5

Pfizer-

BioNTech

Comirnaty

XBB.1.5

Moderna

Spikevax

Moderna

Spikevax

Bivalent

BA.1

Moderna

Spikevax

Bivalent

BA.4/5

Moderna

Spikevax

XBB.1.5

AstraZeneca

Vaxzevria/

COVISHIELD

Janssen

Jcovden

(Johnson

Johnson)

Novavax

Nuvaxovid

All vaccine

products

combined

AESI – Coagulation

disorder (including

thrombotic events)

255

103

463

Bell's Palsy

228

357

Syncope (fainting)

with injury

256

348

Cellulitis

212

286

AESI – Acute

cardiovascular

injury

147

252

Convulsions/

seizure

113

174

Nodule

Thrombocytopenia

†

Paralysis

AESI – Anosmia,

ageusia

Guillain-Barré

syndrome (GBS)†

AESI - Acute liver

injury

AESI - Acute kidney

injury

AESI – TTS/VITT

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 20

Adverse event

Pfizer-

BioNTech

Comirnaty

Pfizer-

BioNTech

Comirnaty

Bivalent

BA.4/5

Pfizer-

BioNTech

Comirnaty

XBB.1.5

Moderna

Spikevax

Moderna

Spikevax

Bivalent

BA.1

Moderna

Spikevax

Bivalent

BA.4/5

Moderna

Spikevax

XBB.1.5

AstraZeneca

Vaxzevria/

COVISHIELD

Janssen

Jcovden

(Johnson

Johnson)

Novavax

Nuvaxovid

All vaccine

products

combined

Oculorespiratory

syndrome (ORS)

Myelitis/transverse

myelitis†

AESI – Single organ

cutaneous

vasculitis

AESI - Subacute

thyroiditis

AESI – Chilblain-like

lesions

AESI - Acute

pancreatitis

AESI -

Rhabdomyolysis

AESI – Erythema

multiforme

AESI - Multisystem

inflammatory

syndrome in

children/adults

Encephalopathy/

encephalitis†

Parotitis

Abscess at the

injection site

(infected)

AESI - Vaccine-

associated

enhanced disease

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 21

Adverse event

Pfizer-

BioNTech

Comirnaty

Pfizer-

BioNTech

Comirnaty

Bivalent

BA.4/5

Pfizer-

BioNTech

Comirnaty

XBB.1.5

Moderna

Spikevax

Moderna

Spikevax

Bivalent

BA.1

Moderna

Spikevax

Bivalent

BA.4/5

Moderna

Spikevax

XBB.1.5

AstraZeneca

Vaxzevria/

COVISHIELD

Janssen

Jcovden

(Johnson

Johnson)

Novavax

Nuvaxovid

All vaccine

products

combined

AESI – Acute

respiratory distress

syndrome

Abscess at the

injection site

(sterile)

Kawasaki Disease

Meningitis

Acute

disseminated

encephalomyelitis

(ADEM)†

Hypotonic-

hyporesponsive

episode (HHE)

Persistent

crying/screaming

Notes:

 The columns above for Pfizer-BioNTech Comirnaty and Moderna Spikevax COVID-19 vaccines include AEFIs associated with all indicated dosages: 3 mcg, 10 mcg and

30 mcg for Pfizer-BioNTech Comirnaty and 25 mcg, 50 mcg and 100 mcg for Moderna Spikevax. Moderna Spikevax BA.1 Bivalent (50 mcg), Moderna Spikevax BA.4/5

Bivalent (50 mcg) and Pfizer-BioNTech Comirnaty Bivalent BA.4/5 (10 mcg and 30 mcg) COVID-19 vaccines are presented separately and were previously

recommended vaccine products before the approval of the XBB.1.5-containing COVID-19 mRNA vaccines. Currently, Pfizer-BioNTech Comirnaty XBB.1.5 and Moderna

Spikevax XBB.1.5 COVID-19 vaccines are approved and recommended for vaccinating individuals who are not previously vaccinated and as additional doses for those

previously vaccinated in approved age groups.

 Novavax Nuvaxovid includes Novavax Nuvaxovid and Novavax Nuvaxovid XBB.1.5 Omicron subvariant COVID-19 vaccines.

 An AEFI report may contain multiple adverse events. Thus the sum of all adverse event-specific counts may not equal to the total number of AEFI reports. Some AEFI

reports did not specify vaccine product received; these are included in the counts for all vaccine products combined.

* This category includes reports of death that are temporally associated with immunization and where no other clear cause of death was established; these reports

should not be interpreted as causally related with vaccine. These reports are described in the Serious AEFI section.

†Represents a medically important event.

Data Source: CCM

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 22

Table A2. Reporting rate per 100,000 doses administered by adverse event and COVID-19 vaccine product: Ontario, December 18, 2020

to May 19, 2024

Adverse event

Pfizer-

BioNTech

Comirnaty

Pfizer-

BioNTech

Comirnaty

Bivalent

BA.4/5

Pfizer-

BioNTech

Comirnaty

XBB.1.5

Moderna

Spikevax

Moderna

Spikevax

Bivalent

BA.1

Moderna

Spikevax

Bivalent

BA.4/5

Moderna

Spikevax

XBB.1.5

AstraZeneca

Vaxzevria/

COVISHIELD

Janssen

Jcovden

(Johnson

Johnson)

Novavax

Nuvaxovid

All vaccine

products

combined

Other severe or

unusual events*

17.8

2.8

1.5

18.2

3.7

2.1

2.7

42.6

274.6

95.9

16.3

Allergic skin

reactions

14.3

2.0

0.8

15.3

2.2

3.5

1.4

25.8

99.9

66.0

13.0

Pain/redness/

swelling at the

injection site

6.7

1.5

1.3

21.9

2.7

5.7

3.9

29.9

74.9

18.0

10.2

Rash

5.8

1.0

0.8

9.1

1.8

2.1

1.3

17.4

74.9

12.0

6.2

Anaesthesia/

paraesthesia

5.1

0.5

0.3

4.1

0.9

0.7

1.2

19.8

149.8

48.0

4.6

Adenopathy/

lymphadenopathy

3.7

0.6

0.2

3.8

0.8

0.7

0.1

4.6

0.0

3.2

Arthritis/arthralgia

3.0

0.5

2.6

1.7

0.0

0.7

9.8

0.0

2.8

Fever in

conjunction with

another reportable

event

2.0

0.3

0.1

4.0

0.8

0.0

0.9

15.7

25.0

18.0

2.6

Severe vomiting/

diarrhea

2.4

0.2

3.1

0.9

0.7

0.1

13.7

25.0

18.0

2.6

AESI - Myocarditis/

pericarditis

2.2

0.2

0.1

3.1

0.3

0.0

0.3

0.8

0.0

12.0

2.1

Event managed as

anaphylaxis†

1.6

0.1

1.3

0.1

0.0

0.1

2.1

25.0

12.0

1.3

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 23

Adverse event

Pfizer-

BioNTech

Comirnaty

Pfizer-

BioNTech

Comirnaty

Bivalent

BA.4/5

Pfizer-

BioNTech

Comirnaty

XBB.1.5

Moderna

Spikevax

Moderna

Spikevax

Bivalent

BA.1

Moderna

Spikevax

Bivalent

BA.4/5

Moderna

Spikevax

XBB.1.5

AstraZeneca

Vaxzevria/

COVISHIELD

Janssen

Jcovden

(Johnson

Johnson)

Novavax

Nuvaxovid

All vaccine

products

combined

AESI – Coagulation

disorder (including

thrombotic events)

1.1

0.4

0.2

1.1

0.9

0.0

0.6

7.0

0.0

1.1

Bell's Palsy

1.0

0.4

0.2

1.0

0.5

0.0

0.3

1.4

0.0

0.9

Syncope (fainting)

with injury

1.1

0.2

0.7

0.2

0.0

0.7

0.0

0.9

Cellulitis

0.2

0.0

0.1

2.2

0.0

0.7

0.3

2.1

0.0

0.7

AESI – Acute

cardiovascular

injury

0.6

0.1

0.0

0.8

0.4

0.0

0.4

1.7

0.0

0.6

Convulsions/seizure

0.5

0.1

0.4

0.1

0.0

1.2

0.0

6.0

0.4

Nodule

0.1

0.0

0.4

0.2

0.0

0.3

1.9

0.0

0.2

Thrombocytopenia

†

0.2

0.0

0.1

0.2

0.7

0.0

1.8

25.0

0.0

0.2

AESI - Acute liver

injury

0.1

0.0

0.1

0.0

0.2

0.0

0.1

AESI - Subacute

thyroiditis

0.1

0.0

0.1

0.0

0.1

0.0

0.1

AESI - TTS/VITT

0.0

1.9

0.0

0.1

AESI – Acute kidney

injury

0.1

0.0

0.1

0.0

0.3

0.0

0.1

AESI – Anosmia,

ageusia

0.1

0.0

0.1

0.0

0.7

0.0

0.4

0.0

0.1

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 24

Adverse event

Pfizer-

BioNTech

Comirnaty

Pfizer-

BioNTech

Comirnaty

Bivalent

BA.4/5

Pfizer-

BioNTech

Comirnaty

XBB.1.5

Moderna

Spikevax

Moderna

Spikevax

Bivalent

BA.1

Moderna

Spikevax

Bivalent

BA.4/5

Moderna

Spikevax

XBB.1.5

AstraZeneca

Vaxzevria/

COVISHIELD

Janssen

Jcovden

(Johnson

Johnson)

Novavax

Nuvaxovid

All vaccine

products

combined

AESI – Chilblain-like

lesions

0.1

0.0

0.1

0.0

0.1

0.0

0.1

AESI – Single organ

cutaneous

vasculitis

0.1

0.0

0.1

0.0

0.4

0.0

0.1

Guillain-Barré

syndrome (GBS)†

0.1

0.0

0.1

0.0

1.6

0.0

0.1

Myelitis/transverse

myelitis†

0.1

0.0

0.1

0.0

0.3

0.0

0.1

Oculorespiratory

syndrome (ORS)

0.1

0.0

0.1

0.0

0.2

0.0

0.1

Paralysis

0.1

0.0

0.1

0.2

0.0

0.8

0.0

0.1

AESI - Acute

pancreatitis

0.1

0.0

0.1

0.0

0.1

0.0

AESI - Multisystem

inflammatory

syndrome in

children/adults

0.0

0.1

0.0

AESI -

Rhabdomyolysis

0.0

0.1

0.2

0.0

0.1

0.0

AESI - Vaccine-

associated

enhanced disease

0.0

AESI – Acute

respiratory distress

syndrome

0.0

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 25

Adverse event

Pfizer-

BioNTech

Comirnaty

Pfizer-

BioNTech

Comirnaty

Bivalent

BA.4/5

Pfizer-

BioNTech

Comirnaty

XBB.1.5

Moderna

Spikevax

Moderna

Spikevax

Bivalent

BA.1

Moderna

Spikevax

Bivalent

BA.4/5

Moderna

Spikevax

XBB.1.5

AstraZeneca

Vaxzevria/

COVISHIELD

Janssen

Jcovden

(Johnson

Johnson)

Novavax

Nuvaxovid

All vaccine

products

combined

AESI – Erythema

multiforme

0.0

0.1

0.0

0.1

0.0

Abscess at the

injection site

(infected)

0.0

0.1

0.0

Abscess at the

injection site

(sterile)

0.0

Acute disseminated

encephalomyelitis

(ADEM)†

0.0

Encephalopathy/

encephalitis†

0.0

0.1

0.0

Hypotonic-

hyporesponsive

episode (HHE)

0.0

Kawasaki Disease

0.0

Meningitis

0.0

0.1

0.0

Parotitis

0.0

Persistent

crying/screaming

0.0

Notes:

 The columns above for Pfizer-BioNTech Comirnaty and Moderna Spikevax COVID-19 vaccines include AEFIs associated with all indicated dosages: 3 mcg, 10 mcg

and 30 mcg for Pfizer-BioNTech Comirnaty and 25 mcg, 50 mcg and 100 mcg for Moderna Spikevax. Moderna Spikevax BA.1 Bivalent (50 mcg), Moderna Spikevax

BA.4/5 Bivalent (50 mcg) and Pfizer-BioNTech Comirnaty Bivalent BA.4/5 (10 mcg and 30 mcg) COVID-19 vaccines are presented separately and were previously

recommended vaccine products before the approval of the XBB1.5-containing COVID-19 mRNA vaccines. Currently, Pfizer-BioNTech Comirnaty XBB.1.5 and

Moderna Spikevax XBB.1.5 COVID-19 vaccines are approved and recommended for vaccinating individuals who are not previously vaccinated and as additional

doses for those previously vaccinated in approved age groups.

Adverse Events Following Immunization (AEFIs) for COVID-19 in Ontario 26

 Novavax Nuvaxovid includes Novavax Nuvaxovid and Novavax Nuvaxovid XBB.1.5 Omicron subvariant COVID-19 vaccines.

 An AEFI report may contain multiple adverse events. Thus the sum of all adverse event-specific counts may not equal to the total number of AEFI reports. Some

AEFI reports did not specify vaccine product received; these are included in the counts for all vaccine products combined.

 Reporting rates for the Janssen Jcovden (Johnson & Johnson) and Novavax Nuvaxovid COVID-19 vaccines should be interpreted with caution due to unstable

reporting rates arising from small number of doses administered.

* This category includes reports of death that are temporally associated with immunization and where no other clear cause of death was established; these reports

should not be interpreted as causally related with vaccine. These reports are described in the Serious AEFI section.

†Represents a medically important event.

Data Source: CCM, COVaxON (see technical notes for details on data sources

Citation

Ontario Agency for Health Protection and Promotion (Public Health Ontario). Adverse events following

immunization (AEFIs) for COVID-19 in Ontario: December 13, 2020 to May 19, 2024. Toronto, ON: King’s

Printer for Ontario; 2024.

Disclaimer

This document was developed by Public Health Ontario (PHO). PHO provides scientific and technical

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Public Health Ontario is an agency of the Government of Ontario dedicated to protecting and promoting

the health of all Ontarians and reducing inequities in health. Public Health Ontario links public health

practitioners, front-line health workers and researchers to the best scientific intelligence and knowledge

from around the world.

For more information about PHO, visit publichealthontario.ca.