RESUMO
BackgroundVaccines against SARS-CoV-2 have been shown to reduce risk of infection, as well as severe disease among those with breakthrough infection, in adults. The latter effect is particularly important as Immune evasion by Omicron variants appears to have made vaccines less effective for prevention of infection. There is currently little available information on the protection conferred by vaccination against severe illness due to SARS-CoV-2 in children. MethodsTo minimize confounding by changing vaccination practices and dominant circulating viral variants, we performed an age- and time-matched nested case-control design. Reported SARS-CoV-2 case records in Ontario children and adolescents aged 4 to 17 were linked to vaccination records. We used multivariable logistic regression to estimate the effectiveness of one and two vaccine doses against hospitalization. ResultsWe identified 130 hospitalized SARS-CoV-2 cases and 1,300 non-hospitalized, age- and time-matched controls, with disease onset between May 28, 2021 and January 9, 2022. One vaccine dose was shown to be 34% effective against hospitalization among SARS-CoV-2 cases (aOR = 0.66 [95% CI: 0.34, 1.21]). In contrast, two doses were 56% (aOR = 0.44 [95% CI: 0.23, 0.83]) effective at preventing hospitalization among SARS-CoV-2 cases. Exploratory instrumental variable analyses, and calculation of E-values, suggested that these effects are unlikely to be explained by unmeasured confounding. ConclusionsEven with immune evasion by SARS-CoV-2 variants, two vaccine doses continue to provide protection against hospitalization among adolescent and pediatric SARS-CoV-2 cases, even when the vaccines do not prevent infection.
RESUMO
BackgroundPregnancy represents a physiological state associated with increased vulnerability to severe outcomes from infectious diseases, both for the pregnant person and developing infant. The SARS-CoV-2 pandemic may have important health consequences for pregnant individuals, who may also be more reluctant than non-pregnant people to accept vaccination. We sought to estimate the degree to which increased severity of SARS-CoV-2 outcomes can be attributed to pregnancy. MethodsOur study made use of a population-based SARS-CoV-2 case file from Ontario, Canada. Due to both varying propensity to receive vaccination, and changes in dominant circulating viral strains over time, a time-matched cohort study was performed to evaluate the relative risk of severe illness in pregnant women with SARS-CoV-2 compared to other SARS-CoV-2 infected women of childbearing age (10 to 49 years old). Risk of severe SARS-CoV-2 outcomes (hospitalization or intensive care unit (ICU) admission) was evaluated in pregnant women and time-matched non-pregnant controls using multivariable conditional logistic regression. ResultsCompared to the rest of the population, non-pregnant women of childbearing age had an elevated risk of infection (standardized morbidity ratio (SMR) 1.28), while risk of infection was reduced among pregnant women (SMR 0.43). After adjustment for age, comorbidity, healthcare worker status, vaccination, and infecting viral variant, pregnant women had a markedly elevated risk of hospitalization (adjusted OR 4.96, 95% CI 3.86 to 6.37) and ICU admission (adjusted OR 6.58, 95% CI 3.29 to 13.18). The relative increase in hospitalization risk associated with pregnancy was greater in women without comorbidities than in those with comorbidities (P for heterogeneity 0.004). InterpretationA time-matched cohort study suggests that while pregnant women may be at a decreased risk of infection relative to the rest of the population, their risk of severe illness is markedly elevated if infection occurs. Given the safety of SARS-CoV-2 vaccines in pregnancy, risk-benefit calculus strongly favours SARS-CoV-2 vaccination in pregnant women.
RESUMO
BackgroundThe rapid development of safe and effective vaccines against the SARS-CoV-2 virus has been a singular scientific achievement. Confounding due to health seeking behaviours and differential testing by vaccination status may bias analyses towards an apparent increase in infection severity following vaccination. We sought to determine whether risks of intensive care unit (ICU) admission and death were diminished significantly by vaccination, even in individuals for whom vaccination failed to prevent hospitalization. MethodsWe used data from Ontario, Canadas Case and Contact Management database, merged to a provincial vaccination dataset (COVaxON) to create a time-matched cohort of individuals who were hospitalized with SARS-CoV-2 infection. Each vaccinated individual was matched to up to five unvaccinated individuals based on test date of positive SARS-CoV-2 infection. Risk of ICU admission and death were evaluated using multivariable conditional logistic regression. Unmatched exploratory analyses were performed to identify sources of heterogeneity in vaccine effects. ResultsIn 20,064 individuals (3,353 vaccinated and 16,711 unvaccinated) hospitalized with infection due to SARS-CoV-2 between January 1st, 2021 and January 5th, 2022, vaccination with 1, 2, or 3 doses significantly reduced the risk of ICU admission and death. An inverse dose-response relationship was observed between vaccine doses received and both outcomes (adjusted odds ratio (aOR) for ICU admission per additional dose: 0.66, 95% CI 0.62 to 0.71; aOR for death per additional dose: 0.78, 95% CI 0.72 to 0.84). The reduction in risk was greater for ICU admission than for death (P for heterogeneity <0.05), but no significant differences in risk were seen based on infecting variant of concern (VOC). InterpretationWe identified a decrease in the risk of ICU admission and death in vaccinated individuals compared to unvaccinated, time-matched controls, even when vaccines failed to prevent infection sufficiently severe to cause hospitalization. Even with diminished efficacy of vaccines against infection with novel VOCs, vaccines remain an important tool for reduction of ICU admission and mortality.
