A Population-Based Test-Negative Matched Case-Control Analysis of SARS-CoV-2 Vaccine Effectiveness Among Pregnant People in Ontario, Canada

Stephanie C Lapinsky; Nancy N Baxter; Rinku Sutradhar; Karl Everett; Joan Porter; Jeffrey C Kwong; Deshayne B Fell; John W Snelgrove; Douglas M Campbell; Andrea N Simpson

doi:10.1016/j.jogc.2023.102239

A Population-Based Test-Negative Matched Case-Control Analysis of SARS-CoV-2 Vaccine Effectiveness Among Pregnant People in Ontario, Canada

J Obstet Gynaecol Can. 2024 Feb;46(2):102239. doi: 10.1016/j.jogc.2023.102239. Epub 2023 Oct 14.

Authors

Affiliations

¹ Department of Obstetrics and Gynaecology, Sunnybrook Health Sciences Centre, Toronto, ON, Canada; Department of Obstetrics and Gynecology, Temerty Faculty of Medicine, University of Toronto, Toronto, ON, Canada; Institute for Clinical Evaluative Sciences, Toronto, ON, Canada. Electronic address: stephanie.lapinsky@mail.utoronto.ca.
² Institute for Clinical Evaluative Sciences, Toronto, ON, Canada; Department of Surgery, University of Toronto, Toronto, ON, Canada; Institute of Health Policy, Management and Evaluation, Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada; Li Ka Shing Knowledge Institute, St. Michael's Hospital, Unity Health Toronto, Toronto, ON, Canada; School of Population and Global Health, University of Melbourne, Melbourne, Victoria, Australia.
³ Institute for Clinical Evaluative Sciences, Toronto, ON, Canada; Institute of Health Policy, Management and Evaluation, Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada.
⁴ Institute for Clinical Evaluative Sciences, Toronto, ON, Canada.
⁵ Institute for Clinical Evaluative Sciences, Toronto, ON, Canada; Dalla Lana School of Public Health, Centre for Vaccine-Preventable Diseases, and Department of Family and Community Medicine, University of Toronto, ON, Canada; Public Health Ontario, Toronto, ON, Canada; University Health Network, Toronto, ON, Canada.
⁶ Institute for Clinical Evaluative Sciences, Toronto, ON, Canada; School of Epidemiology and Public Health, University of Ottawa, Ottawa, ON, Canada; Children's Hospital of Eastern Ontario (CHEO) Research Institute, Ottawa, ON, Canada.
⁷ Institute of Health Policy, Management and Evaluation, Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada; Maternal-Fetal Medicine, Mount Sinai Hospital, Department of Obstetrics & Gynaecology, University of Toronto, Toronto, ON, Canada.
⁸ Li Ka Shing Knowledge Institute, St. Michael's Hospital, Unity Health Toronto, Toronto, ON, Canada; Department of Pediatrics, Faculty of Medicine, University of Toronto, Toronto, ON, Canada; Department of Pediatrics, St Michael's Hospital, Unity Health Toronto, Toronto, ON, Canada.
⁹ Department of Obstetrics and Gynecology, Temerty Faculty of Medicine, University of Toronto, Toronto, ON, Canada; Institute for Clinical Evaluative Sciences, Toronto, ON, Canada; Institute of Health Policy, Management and Evaluation, Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada; Li Ka Shing Knowledge Institute, St. Michael's Hospital, Unity Health Toronto, Toronto, ON, Canada; Department of Obstetrics and Gynecology, St. Michael's Hospital/Unity Health Toronto, Toronto, ON, Canada.

PMID: 37839731
DOI: 10.1016/j.jogc.2023.102239

Abstract

Objective: Pregnancy is a risk factor for severe SARS-CoV-2 infection, which can result in adverse pregnancy outcomes, thus making understanding vaccine effectiveness (VE) in this population important. This study aimed to assess the VE of mRNA COVID-19 vaccines against symptomatic SARS-CoV-2 infection and COVID-19-related hospitalization in pregnant people.

Methods: Population-based matched test-negative case-control study of pregnant people aged 18-49 years, of 12 or more weeks gestation in Ontario, Canada, symptomatic with possible SARS-CoV-2 infection, and having at least 1 positive (n = 1842) or negative (n = 8524) real-time polymerase chain reaction (RT-PCR) SARS-CoV-2 test between December 14, 2020, and December 31, 2021. The exposure was receipt of ≥1 dose of mRNA COVID-19 vaccine versus no vaccination. Exposure was further stratified by number and recency of doses. The primary outcome was a positive SARS-CoV-2 RT-PCR test. As a secondary outcome, VE for COVID-19-related hospitalization was assessed.

Results: In the primary outcome analysis, there were 1821 positive cases, matched to 1821 negative controls. The mean (SD) maternal age was 31 (5) years. When compared to those unvaccinated, receipt of ≥1 dose was associated with an estimated VE of 39% (95% CI 29%-48%) for symptomatic infection, and 85% (95% CI 72%-92%) for COVID-19 hospitalization. VE estimates demonstrated waning with increased time since last vaccination.

Conclusions: mRNA COVID-19 vaccines provide protection against symptomatic COVID-19 illness and are highly effective at preventing severe illness in pregnant people. The observed effect of vaccine waning highlights the importance of booster doses to provide optimal protection for pregnant people.

Keywords: perinatology; pregnancy; severe acute respiratory syndrome-related coronavirus; vaccination; vaccine efficacy.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

COVID-19 Vaccines*
COVID-19* / diagnosis
COVID-19* / epidemiology
COVID-19* / prevention & control
Case-Control Studies
Female
Humans
Ontario / epidemiology
Pregnancy
RNA, Messenger
SARS-CoV-2
Vaccine Efficacy

Substances

COVID-19 Vaccines
RNA, Messenger

Grants and funding

CIHR/Canada