Maternal influenza and Tdap vaccination linked to fewer infant hospital and emergency visits

Maternal vaccination during pregnancy was associated with a substantially lower risk of influenza- and pertussis-related hospitalizations and emergency department (ED) visits among infants younger than 6 months, according to a large population-based cohort study conducted in Italy. The findings provide additional real-world evidence supporting current recommendations for influenza and tetanus-diphtheria-acellular pertussis (Tdap) vaccination during pregnancy and highlight ongoing gaps in maternal vaccine uptake.¹

Infants younger than 6 months are not eligible for influenza vaccination, and those younger than 2 months cannot yet receive Tdap, leaving maternal immunization as the primary strategy for early protection.² While prior studies have demonstrated reductions in infant influenza and pertussis infections following maternal vaccination, fewer investigations have focused specifically on severe outcomes requiring hospital or ED care.

Study design and population

The retrospective cohort study analyzed health care utilization data from the Lombardy region of Italy, which includes approximately 10 million residents covered by the National Health Service. Investigators identified all live-birth pregnancies between January 1, 2018, and November 30, 2022, using linked administrative and clinical databases.

Two separate cohorts were created to assess influenza and Tdap vaccination, respectively. For the influenza cohort, analyses were restricted to births occurring between September and February to align infant follow-up with the influenza season. Pregnant individuals were classified as vaccinated if they received influenza or Tdap vaccination at any point from the last menstrual period through delivery.

Each vaccinated mother-infant dyad was matched 1:1 with an unvaccinated dyad based on month and year of delivery, gestational age at birth, and pregnancy multiplicity. Infants were followed from birth until 6 months of age, occurrence of an outcome event, death, emigration, or the end of the study period.

Outcomes and analysis

The primary outcome was a composite of hospitalization or ED visit with a diagnosis of influenza or pertussis within the first 6 months of life. Cause-specific Cox regression models were used to estimate hazard ratios (HRs), adjusting for maternal sociodemographic and clinical characteristics, as well as the COVID-19 pandemic period. Vaccine effectiveness (VE) was calculated as (1 − HR) × 100%.

Key findings

The influenza cohort included 84,348 mother-infant dyads, of whom 6.4% of pregnant individuals received influenza vaccination. The Tdap cohort included 171,141 dyads, with 41.0% receiving Tdap vaccination during pregnancy.

Infants born to mothers vaccinated against influenza had a significantly lower risk of influenza-related hospitalization or ED visit, with an estimated VE of 69.7% (HR, 0.30; 95% CI, 0.10-0.91). Maternal Tdap vaccination was associated with an 88.6% reduction in pertussis-related hospitalization or ED visit (HR, 0.11; 95% CI, 0.02-0.88).

The authors noted, “Our study provided further evidence of the negative association of maternal influenza and Tdap vaccinations with severe outcomes in infants, specifically 70% and 89% reductions in hospitalization and ED visits for influenza and pertussis, respectively.”

Sensitivity analyses limited to the prepandemic period showed similar protective associations, supporting the robustness of the findings. Additional analyses accounting for infant pertussis vaccination timing and multiple ED visits yielded consistent results.

Vaccination coverage and disparities

Despite free access to both vaccines through Italy’s National Health Service, uptake remained suboptimal, particularly for influenza vaccination. The authors stated, “Despite established recommendations, maternal vaccination coverage remained suboptimal, especially for influenza vaccination.”

Vaccinated pregnant individuals were more likely to be Italian nationals, employed, and have higher educational attainment. These patterns underscore persistent sociodemographic disparities in maternal vaccination acceptance.

Strengths and limitations

A major strength of the study was the use of comprehensive, population-based administrative data, allowing near-complete capture of hospitalizations, ED visits, and vaccination records. The large sample size enabled precise estimates of vaccine effectiveness against severe infant outcomes.

Limitations included potential misclassification of vaccination received outside the public health system and reliance on diagnostic coding for outcome identification. The observational design also limits the ability to fully exclude residual confounding.

Clinical implications

The findings reinforce existing recommendations for influenza and Tdap vaccination during pregnancy as an effective strategy to reduce severe respiratory infections in early infancy. The authors concluded, “These results support the current recommendations for administering these vaccines during pregnancy and highlight the urgent need to implement strategies aimed to increase their acceptance.”

For clinicians caring for pregnant patients, the study provides additional evidence to support counseling efforts focused on maternal vaccination as a means of protecting infants during their most vulnerable months of life.

References

1. Morabito G, Corrao G, Giaquinto C, Cantarutti A, Di Chiara C. Maternal Vaccine Receipt and Infant Hospital and Emergency Visits for Influenza and Pertussis. JAMA Network Open. 2026;9(1):e2553179. doi:https://doi.org/10.1001/jamanetworkopen.2025.53179
2. Rand CM, Olson-Chen C. Maternal vaccination and vaccine hesitancy. Pediatr Clin North Am. 2023;70(2):259-269. doi:10.1016/j.pcl.2022.11.004