The influenza and tetanus, diphtheria, and pertussis (whooping cough; Tdap) vaccines are an estimated 69.7% and 88.6% effective against flu- or pertussis-related hospitalizations or emergency department (ED) visits, respectively, among the infants of vaccinated mothers, although with considerable uncertainty, per an observational study published yesterday in JAMA Network Open.
Researchers in Italy used databases on health care use from the Lombardy region of northern Italy to assess the outcomes of 84,348 mother-infant pairs in a flu cohort and 171,141 pairs in the Tdap cohort from January 2018 to November 2022.
Each vaccinated mother was matched with an unvaccinated peer in the same cohort based on month and year of delivery, gestational age at birth, and pregnancy multiplicity. Most were vaccinated in the third trimester of pregnancy. All infants were younger than six months.
Infants younger than 6 months are too young to receive the flu vaccine, and those younger than 2 months are ineligible for the Tdap vaccine. “Therefore, maternal vaccination during pregnancy represents an effective strategy to confer passive protection to infants and mitigate the risk of infection and severe outcomes in this vulnerable population,” the researchers wrote.
Suboptimal vaccine uptake
In total, 53,448 pregnant women received the Tdap vaccine, and 5,347 were vaccinated against flu. Vaccination uptake was low, with 6.4% receiving the flu vaccine, and 41.0% receiving Tdap. Vaccine acceptance was higher among women who had more education and were employed.
These findings suggest support for the current recommendations for administering the Tdap and influenza vaccines during pregnancy and underline the urgent need to implement strategies to improve their acceptance.
Rates of severe flu and pertussis were 392 and 51 cases per 100,000 person-years, respectively. Infants born to vaccinated mothers were at 70% lower risk for hospitalization or an ED visit for flu (vaccine effectiveness [VE], 69.7%, but with a wide confidence interval [CI], indicating considerable uncertainty) and an 89% lower risk for these outcomes for pertussis (VE, 88.6%, but also with a wide CI).
“These findings suggest support for the current recommendations for administering the Tdap and influenza vaccines during pregnancy and underline the urgent need to implement strategies to improve their acceptance,” the study authors wrote.
They noted that the vaccine coverage was suboptimal, particularly for the flu vaccine. “In this context, providing evidence about vaccine effectiveness and increasing public awareness were particularly important,” they wrote. And the influence of maternal sociodemographic factors “highlighted the importance of implementing targeted public health strategies to improve vaccine uptake, particularly among vulnerable populations who may be less likely to receive vaccinations,” they added.