Study Results Show Flu Vaccination Not Associated With Risk of Adverse Perinatal Outcomes

Influenza vaccination has not associated with an increased risk of adverse perinatal outcomes for those with successive pregnancies, according to results of a study in JAMA Network Open. The study authors said these findings support current recommendations for pregnant individuals or those who might become pregnant during the influenza season.¹

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Currently, the CDC recommends getting vaccination for pertussis, influenza, respiratory syncytial virus, and COVID-19. Some individuals may also be vaccinated for hepatitis B and hepatitis A as per recommendations by their physician. Patients who are pregnant are more likely to have severe illnesses from influenza, and the CDC recommends getting a flu vaccination by the end of October, even though timing of the respiratory season varies.²

According to the study authors, vaccination coverage for the 2022-2023 influenza season was 47.2% in the United States. In the study, investigators aimed to assess whether seasonal flu vaccination in successive pregnancies was associated with an increased risk of adverse outcomes for the second pregnancy as well as the estimated risk associated with the vaccine by length of intervals between pregnancies and the vaccination type.¹

The study was retrospective in nature, including individuals with successive singleton live-birth pregnancies between 2004 and 2018 from 8 health care centers, including Kaiser Permanente (KP) Southern California, Denver Health, HealthPartners Institute, KP Colorado, KP Northern California, NP Northwest, KP Washington, and Marshfield Clinical Research Institute. Investigators included individuals “who had at least 2 successive singleton live-born pregnancies between 20 weeks’ and 42 weeks and 6 days’ gestation.” Investigators excluded those who had an influenza vaccination between May 1 through July 31 and births at less than 20 weeks’ gestation.¹

There were 82,055 people within the same vaccination status for 2 singleton pregnancies included in the study. Approximately 54.69% of individuals had the vaccination in successive pregnancies and 45.31% were unvaccinated in both pregnancies. Of those who were vaccinated, 33.77% were vaccinated in the first trimester. For individuals who were vaccinated, investigators noted that they were more likely to be 30 years or older, tended to have graduated from college with a degree, received more frequent prenatal care, did not smoke or consume alcohol during pregnancy, and received a non-influenza vaccine during the second pregnancy.¹

Compared with individuals who were not vaccinated, those who were had a higher incidence of preeclampsia or eclampsia at 2.95 events per 100 pregnancies compared with 3.39 per 100, preterm premature rupture of membranes at 8,.41 events and 9.51 events, respectively, and chorioamnionitis at 1.69 events and 1.93 events, respectively. In the crude analysis, being vaccinated was associated with an increased risk of preeclampsia or eclampsia and chorioamnionitis; however, after adjusting for potential confounding factors, vaccination was no longer an independent risk factor for any of the outcomes under investigators, according to the investigators.¹

In the adjusted analysis, pregnant individuals who were vaccinated were not at an increased risk of placental abruption, maternal fever, preterm birth, or small for gestational age birth. Furthermore, investigators did not find that the risk of adverse perinatal outcomes differed between either groups for any strata of interpregnancy interval or vaccine type.¹

REFERENCES

1. Getahun D, Liu IA, Sy LS, et al. Safety of the Seasonal Influenza Vaccine in 2 Successive Pregnancies. JAMA Netw Open. 2024;7(9):e2434857. doi:10.1001/jamanetworkopen.2024.34857

2. Vaccine Recommendations Before, During, and After Pregnancy. CDC. 2024. Accessed September 26, 2024. https://www.cdc.gov/vaccines-pregnancy/recommended-vaccines/index.html