Timing of COVID-19 Vaccination and Rates of Severe COVID-19 Infection [ID: 1377384

Abstract

INTRODUCTION: Optimal timing of COVID-19 vaccination in pregnancy is not established. We sought to characterize the relationship between vaccine timing and severe COVID-19 in pregnancy. METHODS: This was a retrospective cohort study of pregnant patients at a tertiary health system December 15, 2020 to June 16, 2022. Severe COVID-19 infection was defined as requiring inpatient admission and remdesivir with or without monoclonals. We compared the rate of severe COVID-19 during pregnancy between patients who were 1) never vaccinated, or were vaccinated 2) before pregnancy, 3) in the first trimester, 4) in the second trimester, or 5) in the third trimester. Infections are reported per 1,000 person-years under observation to account for differences in follow-up and length of gestation. All analyses are descriptive given small numbers of severe infections. RESULTS: Among 17,540 patients, 13,226 (75.2%) were unvaccinated throughout pregnancy. 1,795 (10.2%) were vaccinated before pregnancy, 566 (3.2%) first trimester, 1,126 (6.4%) second trimester, and 825 (4.7%) third trimester. There were 33 cases of severe COVID (27 among unvaccinated patients). No cases occurred among patients vaccinated in the first or second trimester (0 per 1,000 person-years). There were 2 cases among patients vaccinated in the third trimester (3.4 per 1,000 person-years) and 4 cases among patients vaccinated prior to pregnancy (3.3 per 1,000 person-years). All 4 cases among patients vaccinated before pregnancy occurred during the Omicron wave. CONCLUSION: There were fewer severe COVID-19 cases among patients vaccinated early in pregnancy compared to those vaccinated before pregnancy or in the third trimester, suggesting that optimal timing for boosters may be in the first or second trimester, and delaying to the third trimester may increase maternal morbidity. Larger studies are needed to better characterize the relationship between vaccine timing and severe COVID-19.