Background: Pregnant women are at increased risk for influenza-related morbidity. Trivalent inactivated influenza vaccine (TIV) can reduce these risks and is recommended during pregnancy. Concerns regarding safety remain a barrier to vaccine uptake.
Methods: In this retrospective observational cohort study we compared rates of medically attended adverse events between TIV-vaccinated and unvaccinated pregnant women within the Vaccine Safety Datalink. Using generalized estimating equations to account for matching, with a Poisson distribution and log link, we calculated adjusted incident rate ratios (AIRR) for composite safety outcomes for the full cohort and a subset vaccinated during first trimester.
Results: The study cohort included 76,682 vaccinated and 148,578 unvaccinated women matched on age, site, and pregnancy start date; 21,952 (28.6%) women were vaccinated during first trimester. Over a 0-3 day window, receipt of TIV was not associated with increased risk for pre-specified acute medically attended events, including allergic reactions, cellulitis, and seizures (Full cohort AIRR=1.13 (95% CI: 0.82-1.56). First trimester: AIRR=.96 (95% CI: 0.52-1.76)). Over a 1-42 day window, no incident cases of Guillain-Barré syndrome, optic neuritis, transverse myelitis or Bell's palsy following TIV were identified. TIV was not associated with thrombocytopenia (Full cohort: AIRR= 0.89 (95% CI: 0.67-1.2) First trimester: AIRR= .55 (95% CI=0.22-1.4)) or an acute neurologic event (Full cohort: AIRR=0.89 (95% CI=0.52-1.5) First trimester: AIRR= 1.04 (95% CI =0.46-2.4)).
Conclusions: Receipt of TIV during pregnancy was not associated with increased risk for medically attended acute adverse events. These findings support the safety of vaccinating pregnant women against influenza.