An observational study published in JAMA Network Open estimated the effectiveness of influenza and tetanus, diphtheria, and pertussis (Tdap) vaccines in preventing flu- or pertussis-related hospitalizations or emergency department (ED) visits among infants of vaccinated mothers. The study estimated 69.7% effectiveness for flu vaccines and 88.6% for Tdap, with noted uncertainty in the findings.
Researchers in Italy utilized health care usage databases from the Lombardy region. The study assessed outcomes for 84,348 mother-infant pairs in a flu cohort and 171,141 pairs in a Tdap cohort, covering January 2018 to November 2022. Each vaccinated mother was matched with an unvaccinated peer based on delivery month/year, gestational age, and pregnancy multiplicity. Most vaccinations occurred in the third trimester of pregnancy, and all infants were under six months old.
Infants younger than six months cannot receive the flu vaccine, and those under two months are ineligible for the Tdap vaccine. Maternal vaccination during pregnancy is therefore considered a strategy to provide passive protection to infants and reduce infection risk in this vulnerable population.
Overall, 53,448 pregnant women received the Tdap vaccine, and 5,347 received the flu vaccine. Vaccine uptake was 6.4% for the flu vaccine and 41.0% for Tdap, indicating suboptimal coverage. Higher vaccine acceptance was observed among women with more education and employment.
Infants born to vaccinated mothers showed a 70% lower risk for hospitalization or an ED visit due to flu and an 89% lower risk for these outcomes related to pertussis. These findings support current recommendations for administering Tdap and influenza vaccines during pregnancy. The study authors emphasized the need to implement strategies to improve vaccine acceptance, especially given the suboptimal coverage, and highlighted the importance of targeted public health strategies to increase uptake among vulnerable populations.