Cohort event monitoring of booster COVID-19 vaccine safety using patient-reported outcomes in pregnant women.

Background: COVID-19 vaccination is still accepted by only half of pregnant women. Further scientific evidence on the safety of the COVID-19 vaccine could help overcome vaccine hesitancy in this population. Objectives: The aim of this study is to describe and compare the incidence of solicited and unsolicited adverse drug reactions (ADRs) and serious adverse reactions following the booster dose of different COVID-19 vaccines in pregnant women versus the general female population. Methods: We conducted a web-based prospective observational cohort study. In eight European countries, pregnant women and non-pregnant women from the same source population who received a first or second booster dose of COVID-19 vaccine between February 2021 and February 2023 were included in the study if they registered within 48 h after vaccination and completed at least the baseline questionnaire and one follow-up questionnaire. The exposure was a mRNA COVID-19 vaccine of different brands used for a booster dose. The proportion of solicited and unsolicited ADRs following the booster dose by vaccine brand was computed across participating countries in pregnant and non-pregnant women. We performed descriptive analyses of medical characteristics of vaccinees. We compared the proportions of local and systemic solicited ADRs and unsolicited ADRs in pregnant vaccinees with a random sample (1:4 ratio) of age- and vaccine brand-matched vaccinees from the general female population. Results: Overall, 358 pregnant women were matched with 1,432 women from the general population. The proportion of women who reported at least one solicited adverse event was significantly lower in the pregnant group in the non-pregnant group (56.4% [95%CI 51.3%-61.5%] versus 72.3% [95%CI 70.0%-74.6%], p = 0.01). Regarding local ADRs, pregnant women reported significantly less pain and swelling. As for systemic ADRs, pregnant women reported all symptoms less frequently than non-pregnant women, except nausea. The proportion of women who reported at least one unsolicited adverse event was less frequent in the pregnant group (7.8% [95%CI 5.0%-10.6%] versus 24.9% [95%CI 22.7%-27.1%], p = 3.10 Conclusion: This prospective study on COVID-19 vaccine safety monitoring showed that pregnant women from the general population reported solicited and unsolicited ADRs less frequently than non-pregnant women.