Vaccination Against COVID-19 in Expecting Mothers Significantly Lowers Hospitalization and Preterm Birth Risks Amidst Variants
The impact of COVID-19 vaccination during pregnancy is profound, as it significantly reduces the chances of hospitalization and preterm births, offering essential insights for maternal healthcare strategies.
A recent study published in JAMA reveals that if the vaccine is received before a contraction of the virus, the likelihood of adverse outcomes, including preterm birth, decreases across all variants of the virus. This research highlights the critical importance of vaccination for pregnant individuals—irrespective of which variant they may encounter.
Understanding the Impact of COVID-19 Variants and Vaccination on Expectant Mothers
Despite existing knowledge about certain clinical and demographic factors that elevate the risk of severe COVID-19 during pregnancy, the specific risks posed by different variants and how vaccination might mitigate these risks remain unclear. This ambiguity arises from the simultaneous emergence of new variants and the implementation of vaccination programs.
Prior studies focusing on vaccination have demonstrated a protective effect against negative maternal and infant outcomes following COVID-19 infections. However, many of these earlier investigations suffered from limited sample sizes, resulting in a lack of comprehensive understanding regarding how various variants and vaccination statuses independently affect outcomes in larger, prospective groups.
To fill this knowledge gap, researchers evaluated data from the Canadian Surveillance of COVID-19 in Pregnancy program. This program tracks maternal and infant outcomes related to COVID-19 during pregnancy, examining how vaccination influences adverse outcomes.
The study encompassed pregnant individuals diagnosed with COVID-19 between April 5, 2021, and December 31, 2022, across nine provinces and territories in Canada: British Columbia, Alberta, Manitoba, Ontario, Quebec, New Brunswick, Prince Edward Island, Nova Scotia, and Yukon. The follow-up extended into 2023 to ensure thorough capture of pregnancy results and infant health outcomes.
How COVID-19 Vaccination Mitigates Negative Pregnancy Outcomes
Out of 26,584 cases identified in the study, vaccination status was determined for 19,899 participants. The majority were from Ontario (n = 13,679), followed by Alberta (n = 2514), British Columbia (n = 1813), Quebec (n = 977), Manitoba (n = 386), Prince Edward Island (n = 308), Nova Scotia (n = 159), New Brunswick (n = 60), and Yukon (n < 6).
In total, 69.2% (n = 13,799) of the infections occurred during the Omicron variant wave, while 30.8% (n = 6120) were during the Delta variant wave. Among the women studied, 46.3% (n = 8763) were aged between 30 and 35 years, which corresponds with the average maternal age in Canada, and 55.9% (n = 4765) identified as White.
Moreover, 72.2% (n = 14,367) of the COVID-19 cases involved participants who had received at least one dose of the vaccine before their diagnosis, leaving 27.8% (n = 5532) unvaccinated. Of those who had been vaccinated, 20% (n = 2942) received the vaccine while pregnant, typically around 18 weeks (interquartile range, 11-25 weeks) prior to their COVID-19 diagnosis. Generally, vaccinated individuals tended to be older, mostly White, had lower body mass index levels, and exhibited decreased rates of gestational hypertension; however, they did have higher incidences of preexisting and gestational diabetes.
Throughout both the Delta and Omicron waves, vaccination was linked to a reduced need for hospitalization (Delta: relative risk [RR], 0.38 [95% confidence interval (CI), 0.30-0.48]; absolute risk difference [ARD], 8.7% [95% CI, 7.3%-10.2%]; Omicron: RR, 0.38 [95% CI, 0.27-0.53]; ARD, 3.8% [95% CI, 2.4%-5.2%]), fewer admissions to critical care units (Delta: RR, 0.10 [95% CI, 0.04-0.29]; ARD, 2.4% [95% CI, 1.8%-2.9%]; Omicron: RR, 0.10 [95% CI, 0.03-0.29]; ARD, 0.85% [95% CI, 0.27%-1.44%]), and a decrease in preterm births (Delta: RR, 0.80 [95% CI, 0.66-0.98]; ARD, 1.8% [95% CI, 0.3%-3.4%]; Omicron: RR, 0.64 [95% CI, 0.52-0.77]; ARD, 4.1% [95% CI, 2.0%-6.2%]).
Further analyses confirmed that the link between vaccination and lower hospitalization rates persisted through both periods, even after accounting for other health conditions. In comparison to vaccinated patients, those who were unvaccinated faced a significantly higher risk of hospitalization, with an adjusted RR of 2.43 (95% CI, 1.72-3.43) during the Omicron variant period and 3.82 (95% CI, 2.38-6.14) during the Delta period.
Guiding Future Strategies on COVID-19 Vaccination and Maternal Care
The researchers also acknowledged certain limitations within their study. They pointed out that there was a decline in formal tracking of COVID-19 cases by public health authorities during the Omicron wave, which likely resulted in some missed cases. Furthermore, as an observational study, causation cannot be definitively established. Nevertheless, the authors expressed confidence in the significance of their findings for clinical practice.
They concluded, "This detailed analysis of the relationship between vaccination status and reduced negative outcomes during both the Delta and Omicron waves sheds new light on the role of vaccination throughout the COVID-19 pandemic."
References:
1. McClymont E, Blitz S, Forward L, et al. The role of vaccination in maternal and perinatal outcomes associated with COVID-19 in pregnancy. JAMA. Published online December 15, 2025. doi:10.1001/jama.2025.21001
2. Canadian surveillance of COVID-19 in pregnancy: epidemiology, maternal and infant outcomes. University of British Columbia. Updated September 13, 2023. Accessed December 15, 2025. https://ridprogram.med.ubc.ca/cancovid-preg/
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