This is a summary, written by members of the CITF Secretariat, of:

Bettinger JA, Irvine MA, Shulha HP, Valiquette L, Muller MP, Vanderkooi OG, Kellner JD, Top KA, Sadarangani M, McGeer A, Isenor JE, Marty K, Soe P, De Serres G; Canadian Immunization Research Network. Adverse Events Following Immunization with mRNA and Viral Vector Vaccines in Individuals with Previous SARS-CoV-2 Infection from the Canadian National Vaccine Safety Network. Clin Infect Dis. 2022 Oct 31:ciac852. doi: 10.1093/cid/ciac852.

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

A CITF and Canadian Immunization Research Network (CIRN) funded study, published in Clinical Infectious Diseases, showed that adults who had a previous moderate or severe SARS-CoV-2 infection were more likely to experience side effects from the first vaccine doses. More specifically, they were more likely to have a health event sufficient to impact routine activities or require medical assessment in the week following each of the first three vaccine doses. The study was led by Dr. Julie Bettinger (BC Children’s Hospital).

2.6% of vaccinated individuals in the study (18,127 of 684,998) reported a prior SARS-CoV-2 infection. The infection occurred, on average, four months prior to vaccination.

Key takeaways:

  • People who had previous moderate (bedridden) to severe (hospitalized) COVID-19 had higher odds of a health event preventing daily activities (i.e., resulting in work absenteeism or requiring medical consultation) after dose 1.
  • After one dose of vaccine, events of a severity sufficient to prevent daily activities, result in work or school absenteeism, or require medical consultation was observed for all three vaccine types (Pfizer, Moderna, and AstraZeneca) – at a rate of 12% to 16% for the previously infected vs. 3% to 12% for the uninfected. But a higher percentage of previously infected participants reported serious adverse effects from immunization (emergency room or hospitalization)- 0.6% to 0.7% among previously infected compared with 0.2% to 0.5% among the non-infected.
  • Following 2 or 3 doses of the vaccines, an increase in side effects associated with previous infection was present, but was less compared to after the first dose.
  • People who had had mild or asymptomatic infections did not experience more side effects interrupting daily activity after any vaccine dose.

The researchers conclude that, for all three doses, health events that prevent work, daily activities or require medical care were more likely to occur in the first week after initiation of COVID-19 vaccination in individuals with a prior moderate to severe SARS-CoV-2 infection. These events occurred more frequently after Moderna than Pfizer, regardless of dose.  The same association did not occur among those with a mild or asymptomatic previous infection. They recommend that healthcare providers consider additional vaccine counseling on expected adverse effects when dealing with individuals who were infected with SARS-CoV-2 prior to vaccination.

The study assessed 684,998 vaccinated participants recruited from Ontario, Quebec, British Columbia, Alberta, Nova Scotia, Yukon, and Prince Edward Island. These provinces account for >75% of the Canadian population.  As of November 27th, 2021, all participants completed their dose 1: 369,406 received Pfizer, 201,314 received Moderna, and 113,127 got AstraZeneca. A median of two months elapsed between the first and the second dose. As of February 20, 2022, 120,758 vaccinated participants had completed their third dose survey – 43,755 received Pfizer, and 76,795 received Moderna. The interval between doses two and three was at least 6 months, as per provincial guidelines.