Associate Professor University of San Francisco, San Francisco CA, USA, United States
Background: Compared to non-pregnant adults, pregnant people are at greater risk of complications from COVID-19 and are therefore a priority group for immunization. Epidemiological studies continue to support the safety of vaccination during pregnancy with mRNA COVID-19 vaccines; however, few studies have investigated the safety of vaccination with an adenoviral vector COVID-19 vaccine (Johnson & Johnson/Janssen® in the U.S.) during pregnancy, creating a critical knowledge gap for global vaccine provision for pregnant people.
Objectives: To compare the rate of adverse events of special interest associated with adenoviral vector vaccine exposure during pregnancy as compared to a) non-pregnant women of reproductive age exposed to adenoviral vector vaccine; b) pregnant people who received mRNA COVID-19 vaccine; and c) unvaccinated pregnant people.
Methods: We constructed a claims-based cohort study using the Merative® Marketscan® Commercial Database and Multi-State Medicaid Database, which includes health insurance claims for outpatient and inpatient care for privately and publicly insured U.S. individuals. We included all pregnancies with a date of pregnancy end from February 27, 2020 (date of Janssen® authorization) through September 30, 2021, using a previously validated algorithm to identify pregnancy outcomes. We classed pregnancies as vaccinated if they had a date of Janssen® vaccination during pregnancy. We searched outpatient and inpatient medical claims records for ICD-coded pregnancy-related and post-vaccination events, including thrombosis or thrombocytopenia during pregnancy. Adenoviral vector vaccine exposed pregnancies were time-matched comparators (1:4) and relative risk was estimated using log-binomial regression.
Results: Preliminary analyses of144,724 eligible pregnancies indicated that 436 (0.3%) pregnancies were exposed to an adenoviral vector COVID-19 vaccine; 50% of adenoviral vector vaccinations occurred during the third trimester, and 36% occurred during second trimester; 83% of unvaccinated and 80% of adenoviral vector vaccinated pregnancies ended in live birth. We identified no cases of ICD-coded thrombosis or thrombocytopenia in adenoviral vector vaccinated individuals and 93 cases among unvaccinated pregnant people.
Conclusions: These initial results highlight the ability to use large medical claims records to investigate the health effects of uncommon vaccine exposures during pregnancy. Given the small number of exposures, multi-country studies will likely be needed to comprehensively evaluate the risk of rare outcomes associated with adenoviral vector COVID-19 vaccination during pregnancy.