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.

BACKGROUND: Adults previously infected with SARS-CoV-2 develop short-term immunity and may have increased reactogenicity to COVID-19 vaccines. This prospective, multi-center active surveillance cohort study examined the short-term safety of COVID-19 vaccines in adults with a prior history of SARS-CoV-2. METHODS: Canadian adults vaccinated between December 22, 2020 and November 27, 2021 were sent an electronic questionnaire 7 days post dose 1, dose 2 and dose 3 vaccination. The main outcome was health events occurring in the first 7 days after each vaccination that prevented daily activities, resulted in work absenteeism or required a medical consultation, including hospitalization. RESULTS: Among 684,998 vaccinated individuals, 2.6% (18,127/684,998) reported a prior history of SARS-CoV-2 infection a median of 4 months (interquartile range 2-6 months) previously. After dose 1, individuals with moderate (bedridden) to severe (hospitalized) COVID-19 who received BNT162b2, mRNA1273 or ChAdox1-S vaccines had higher odds of a health event preventing daily activities, resulting in work absenteeism or requiring medical consultation; adjusted odds ratio (AOR) 3.96 (95% CI 3.67-4.28) for BNT162b2, 5.01 (4.57-5.50) for mRNA1273 and 1.84 (1.54-2.20) for ChAdox1-S compared to no infection. Following dose 2 and 3, the greater risk associated with previous infection was also present but attenuated compared to dose 1. For all doses, the association was lower or absent after mild or asymptomatic infection. CONCLUSION: Adults with moderate or severe previous SARS-CoV-2 infection were more likely to have a health event sufficient to impact routine activities or require medical assessment in the week following each vaccine doses.

Child transmission of SARS-CoV-2: a systematic review and meta-analysis.

BACKGROUND: Understanding of the role of children in COVID-19 transmission has significant implications for school and childcare policies, as well as appropriate targeting of vaccine campaigns. The objective of this systematic review was to identify the role of children in SARS-CoV-2 transmission to other children and adults. METHODS: MEDLINE, EMBASE, CINAHL, Cochrane Central Register of Controlled Trials, and Web of Science were electronically searched for articles published before March 31, 2021. Studies of child-to-child and child-to-adult transmission and quantified the incidence of index and resulting secondary attack rates of children and adults in schools, households, and other congregate pediatric settings were identified. All articles describing confirmed transmission of SARS-CoV-2 from a child were included. PRISMA guidelines for data abstraction were followed, with each step conducted by two reviewers. RESULTS: 40 of 6110 articles identified met inclusion criteria. Overall, there were 0.8 secondary cases per primary index case, with a secondary attack rate of 8.4% among known contacts. The secondary attack rate was 26.4% among adult contacts versus 5.7% amongst child contacts. The pooled estimate of a contact of a pediatric index case being infected as secondary case was 0.10 (95% CI 0.03-0.25). CONCLUSIONS: Children transmit COVID-19 at a lower rate to children than to adults. Household adults are at highest risk of transmission from an infected child, more so than adults or children in other settings.

Safety of COVID-19 vaccines in pregnancy: a Canadian National Vaccine Safety (CANVAS) network cohort study.

BACKGROUND: Pregnant individuals have been receiving COVID-19 vaccines following pre-authorisation clinical trials in non-pregnant people. This study aimed to determine the frequency and nature of significant health events among pregnant females after COVID-19 vaccination, compared with unvaccinated pregnant controls and vaccinated non-pregnant individuals. METHODS: We did an observational cohort study, set in seven Canadian provinces and territories including Ontario, Quebec, British Columbia, Alberta, Nova Scotia, Yukon, and Prince Edward Island. Eligibility criteria for vaccinated individuals were a first dose of a COVID-19 vaccine within the previous 7 days; an active email address and telephone number; ability to communicate in English or French; and residence in the aforementioned provinces or territories. Study participants were pregnant and non-pregnant females aged 15-49 years. Individuals were able to participate as controls if they were unvaccinated and fulfilled the other criteria. Data were collected primarily by self-reported survey after both vaccine doses, with telephone follow-up for those reporting any medically attended event. Participants reported significant health events (new or worsening of a health event sufficient to cause work or school absenteeism, medical consultation, or prevent daily activities) occurring within 7 days of vaccination or within the past 7 days for unvaccinated individuals. We employed multivariable logistic regression to examine significant health events associated with mRNA vaccines, adjusting for age group, previous SARS-CoV-2 infection, and trimester, as appropriate. FINDINGS: As of Nov 4, 2021, 191 360 women aged 15-49 years with known pregnancy status had completed the first vaccine dose survey and 94 937 had completed the second dose survey. 180 388 received one dose and 94 262 received a second dose of an mRNA vaccine, with 5597 pregnant participants receiving dose one and 3108 receiving dose two, and 174 765 non-pregnant participants receiving dose one and 91 131 receiving dose two. Of 6179 included unvaccinated control participants, 339 were pregnant and 5840 were not pregnant. Overall, 226 (4·0%) of 5597 vaccinated pregnant females reported a significant health event after dose one of an mRNA vaccine, and 227 (7·3%) of 3108 after dose two, compared with 11 (3·2%) of 339 pregnant unvaccinated females. Pregnant vaccinated females had an increased odds of a significant health event within 7 days of the vaccine after dose two of mRNA-1273 (adjusted odds ratio [aOR] 4·4 [95% CI 2·4-8·3]) compared with pregnant unvaccinated controls within the past 7 days, but not after dose one of mRNA-1273 or any dose of BNT162b2. Pregnant vaccinated females had decreased odds of a significant health event compared with non-pregnant vaccinated females after both dose one (aOR 0·63 [95% CI 0·55-0·72]) and dose two (aOR 0·62 [0·54-0·71]) of any mRNA vaccination. There were no significant differences in any analyses when restricted to events which led to medical attention. INTERPRETATION: COVID-19 mRNA vaccines have a good safety profile in pregnancy. These data can be used to appropriately inform pregnant people regarding reactogenicity of COVID-19 vaccines during pregnancy, and should be considered alongside effectiveness and immunogenicity data to make appropriate recommendations about best use of COVID-19 vaccines in pregnancy. FUNDING: Canadian Institutes of Health Research, Public Health Agency of Canada.