Association Between Influenza Vaccination and SARS-CoV-2 Infection.

Background: Recent data in nonpregnant individuals suggest a protective effect of influenza vaccination against SARS-CoV-2 infection and its severity.

Objectives: Our primary objective was to evaluate whether influenza vaccination was associated with COVID-19 severity and pregnancy and neonatal outcomes among those infected with SARS-CoV-2. The secondary objective was to examine the association between influenza vaccination and SARS-CoV-2 infection.

Study Design: Secondary analysis of a multicenter retrospective cohort of pregnant people who tested positive for SARS-CoV-2 between March and August 2020, and a cohort of random deliveries during the same time period. The associations between 2019 influenza vaccination and the primary outcome of moderate-to-critical COVID-19 as well as maternal and perinatal outcomes were examined among all people who tested positive for SARS-CoV-2 between March and August 2020. The association between 2019 influenza vaccination and having a positive SARS-CoV-2 test was examined among a cohort of individuals who delivered on randomly selected dates between March and August 2020. Univariable and multivariable analyses were performed.

Results: Of 2325 people who tested positive for SARS-CoV-2, 1068 (45.9%) were vaccinated against influenza in 2019. Those who received the influenza vaccine were older, leaner, more likely to have private insurance, and identify as White or Hispanic. They were less likely to smoke tobacco and identify as Black. Overall, 419 (18.0%) had moderate, 193 (8.3%) severe, and 52 (2.2%) critical COVID-19. There was no association between influenza vaccination and moderate-to-critical COVID-19 (29.2% vs. 28.0%, adjusted OR 1.10, 95% CI 0.90-1.34) or adverse maternal and perinatal outcomes among those who tested positive. Of 8152 people who delivered in 2020, 4658 (57.1%) received the influenza vaccine. Prior vaccination was not associated with a difference in the odds of SARS-CoV-2 infection (3.8% vs. 4.2%, adjusted OR 0.94, 95% CI 0.74-1.19).

Conclusion: Prior influenza vaccination was not associated with decreased severity of COVID-19 or lower odds of SARS-CoV-2 infection in pregnancy.