Studies Examining Maternal Vaccination Decisions and Influenza Burden in U.S. Infants Ages 0-5 Months

Abstract

Introduction Pregnant women and young infants are particularly vulnerable to respiratory viral infections, but infants aged 0-5 months cannot receive COVID-19 and influenza vaccines, making maternal vaccination a key prevention strategy. We examined changes in rates of maternal COVID-19 and influenza vaccination, influenza-associated hospitalization burden and characteristics of influenza positive infants aged 0-5 months by acute care setting. Methods Data from two health systems and a surveillance network were analyzed. Study 1 examined COVID-19 and influenza vaccination patterns between two temporal cohorts of pregnant women (2021-2023, n=5,949). Study 2 compared characteristics of influenza-positive and influenza-negative hospitalized infants aged 0-5 months and calculated an influenza hospitalization rate for this age group from 2016-2020 (n=2,605). Study 3 compared infants with laboratory-confirmed influenza discharged from the emergency department versus hospitalized (n=210). Results In Study 1, COVID-19 vaccinations fell substantially between the two cohorts (62% to 26%), while influenza vaccination showed a lesser decline (52% vs 48%). Those receiving neither vaccine increased (26% to 44%). Study 2 found influenza-positive infants had less severe illness than influenza negative infants, 79% of whom tested positive for other viral pathogens. The calculated influenza hospitalization rate was 129.5 per 100,000 infants. Study 3 identified younger age and underlying condition as associated with hospitalization (aOR 4.37, 95% CI 2.11-9.06, aOR 6.29, 95% CI 2.34-16.86). Public insurance and higher maternal education had lower odds (aOR 0.12, 95% CI 0.04-0.34), aOR 0.36, 95% CI 0.14-0.91). Conclusion Our calculated influenza hospitalization rate (2016-2020) was significantly lower than historical estimates from the 2000s, coinciding temporally with increased national maternal influenza vaccination coverage. Our analysis of influenza among infants aged 0-5 months demonstrated that influenza comprised a small proportion of acute respiratory illness hospitalizations. Maternal vaccination patterns revealed declines in uptake of both vaccines between 2021-2023, with COVID-19 vaccination showing the steepest decrease. Considering recent national declines in maternal influenza vaccination, our findings underscore the importance of developing targeted interventions to improve maternal vaccination coverage and sustain reduced influenza hospitalization burden in this age group.