Effectiveness of BNT162b2 and mRNA-1273 COVID-19 vaccines against symptomatic SARS-CoV-2 infection and severe COVID-19 outcomes in Ontario, Canada: a test-negative design study

Abstract

Objectives To estimate the effectiveness of one and two doses of mRNA COVID-19 vaccines against symptomatic infection and severe outcomes. Design Using a test-negative design study and linked laboratory, vaccination, and health administrative databases, we estimated adjusted vaccine effectiveness (aVE) against symptomatic infection and severe outcomes (hospitalization or death) using multivariable logistic regression. Setting Ontario, Canada between 14 December 2020 and 19 April 2021. Participants Community-dwelling adults aged ≥16 years who were tested for SARS-CoV-2 and had COVID-19 symptoms. Interventions Pfizer-BioNTech’s BNT162b2 or Moderna’s mRNA-1273 vaccine. Main outcome measures Laboratory-confirmed SARS-CoV-2 identified by RT-PCR; hospitalization or death associated with SARS-CoV-2 infection. Results Among 324,033 symptomatic individuals, 53,270 (16.4%) were positive for SARS-CoV-2 and 21,272 (6.6%) received ≥1 vaccine dose. Among test-positive cases, 2,479 (4.7%) had a severe outcome. aVE against symptomatic infection ≥14 days after receiving only 1 dose was 60% (95%CI, 57 to 64%), increasing from 48% (95%CI, 41 to 54%) at 14–20 days after the first dose to 71% (95%CI, 63 to 78%) at 35–41 days. aVE ≥7 days after receiving 2 doses was 91% (95%CI, 89 to 93%). Against severe outcomes, aVE ≥14 days after receiving 1 dose was 70% (95%CI, 60 to 77%), increasing from 62% (95%CI, 44 to 75%) at 14–20 days to 91% (95%CI, 73 to 97%) at ≥35 days, whereas aVE ≥7 days after receiving 2 doses was 98% (95%CI, 88 to 100%). For adults aged ≥70 years, aVE estimates were lower after receiving 1 dose, but were comparable to younger adults after 28 days. After 2 doses, we observed high aVE against E484K-positive variants. Conclusions Two doses of BNT162b2 and mRNA-1273 vaccines are highly effective against both symptomatic infection and severe outcomes. Effectiveness is lower after only a single dose, particularly for older adults shortly after the first dose.