Abstract
Background
Pregnant women are recommended to receive COVID-19 vaccines; however, relative effectiveness of vaccination by pregnancy status is unclear.
Methods
We compared the relative effectiveness of mRNA COVID-19 vaccines according to whether women received both while pregnant (n= 7,412), one dose while pregnant (n = 3,538), both while postpartum (n = 1,856), or both doses while neither pregnant nor postpartum (n = 6,687). We estimated risk of SARS-CoV-2 infection starting 14 days after the second dose using Cox regression, reporting hazard ratios (HR) and 95% confidence intervals (CI). Secondly, we examined relative effectiveness of a third (booster) dose while pregnant compared to outside pregnancy. The major circulating variant during the study period was the Delta variant.
Results
54% of women received two doses of the BNT162b2 vaccine, 16% received two doses of the mRNA-1273 vaccine, while 30% receiv ed one dose of both vaccines. Compared to women who received both doses while neither pregnant nor postpartum, the adjusted HR for a positive SARS-CoV-2 PCR test was similar if the woman received both doses while pregnant (1.04; 95% CI: 0.94, 1.17), one dose while pregnant and one dose before or after pregnancy (1.03; 95% CI: 0.93, 1.14), or both doses while postpartum (0.99; 95% CI: 0.92, 1.07). The findings were similar for BNT162b2 (Pfizer-BioNTech Comirnaty) and mRNA-1273 (Moderna Spikevax), and during Delta- and Omicron-dominant periods. We observed no differences in the relative effectiveness of the booster dose according to pregnancy status.
Conclusions
We observed similar effectiveness of mRNA vaccines against SARS-CoV-2 infection among women regardless of pregnancy status at the time of vaccination.
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