(348) MotherToBaby Pregnancy Studies, Vaccines in Medications Surveillance System (VAMPSS) COVID-19 Vaccines Study

Background: Pregnant people are particularly vulnerable to SARS-CoV-2 and at risk of developing a more complicated disease course, including increased risk of maternal death and other adverse pregnancy outcomes. These data would provide essential safety and efficacy information that would support public health recommendations in this special population.

Objectives: To describe preliminary results for among pregnancy registry participants enrolled in MotherToBaby Pregnancy Studies.

Methods: This study used data from the Organization of Teratology Information Specialists (OTIS) Pregnancy Registry as part of the Vaccines and Medications in Pregnancy Surveillance System (VAMPSS) which enrolls pregnant women residing in the US or Canada. Data on exposures, outcomes and covariates were captured through maternal interviews and medical records. The study population included Registry participants who met eligibility criteria on or after December 11, 2020. Pregnant women who received any dose of a COVID-19 vaccine from 30 days prior to the last menstrual period through the end of pregnancy were compared to pregnant women who received no COVID-19 vaccine in pregnancy.

Results: Among pregnant women participating in the Registry through 17 July 2023, 1,310 were enrolled in the COVID-19 vaccine exposure cohort, of which 1,203 were exposed to an mRNA vaccine. A total of 1,208 participants were enrolled in the comparator cohort. As of the datacut, 1,148 (87.6%) in the vaccine exposure cohort and 713 (59.0%) in the comparator cohort had completed pregnancies.

Descriptive data indicated similar percentages of pregnancies ending in at least one live born infant by trimester of first vaccine dose (93.8% to 98.5% in the exposed cohort vs. 95.1% in the comparator group). The left truncated accounted spontaneous abortion rate in those enrolled prior to 20 weeks’ gestation was 0.0% to 9.2% in exposed vs. 26.6% in the comparator. The preliminary data on proportion of pregnancies ending in at least one live born infant with a major birth defect identified at birth indicated 14/514 (2.7%) among those with a vaccine dose in the first trimester compared to 15/678 (2.2%) in the comparator group. There were 2 stillbirths and no elective terminations reported in the exposed group, compared to 4 stillbirths and 1 elective termination reported in the comparison group. Lost to follow-up rates ranged from 1.1% to 4.5% across cohorts.

Conclusions: Preliminary data have not identified any new safety concerns for COVID-19 vaccines during pregnancy. When capture of pregnancy outcomes and one-year follow-up for the full study is completed, adjusted statistical comparisons will be performed.