Significant reductions in influenza- and pertussis-related hospitalisations and emergency department attendances have been observed among infants younger than six months born to mothers vaccinated against influenza and tetanus-diphtheria-acellular pertussis (Tdap) during pregnancy.

Published in JAMA Network Open, the large population-based cohort study, led by the University of Milano-Bicocca, aimed to evaluate the association between maternal influenza and Tdap vaccination in pregnancy and severe influenza- and pertussis-related outcomes in early infancy.

Using linked healthcare utilisation databases, the researchers identified all live-birth pregnancies between January 2018 and November 2022. After applying eligibility criteria, 84,348 mother-infant dyads were included in the influenza cohort and 171,141 in the Tdap cohort.

Influenza vaccination coverage during pregnancy was 6.4% (5,359 vaccinated), while Tdap coverage was 41.0% (70,119 vaccinated). Successful matching yielded 5,347 and 53,448 vaccinated-unvaccinated pairs, respectively.

Infants were followed from birth to six months of age, or until hospitalisation or emergency department attendance for influenza or pertussis, death, emigration or study end. The incidence of severe influenza was 392 cases per 100,000 person-years and for pertussis it was 51.

Reduced risk of infant hospitalisation

Maternal influenza vaccination was associated with a reduced risk of infant influenza-related hospitalisation or emergency department visit (adjusted hazard ratio [HR] 0.30; 95% CI 0.10–0.91), corresponding to a vaccine effectiveness of 69.7% (95% CI 8.7%–90.0%).

Maternal Tdap vaccination was similarly associated with a lower risk of pertussis-related hospitalisation or emergency department attendance (adjusted HR 0.11; 95% CI 0.02–0.88), equating to a vaccine effectiveness of 88.6% (95% CI 11.5%–98.5%).

Sensitivity analyses restricted to the pre-pandemic period and alternative modelling approaches produced consistent findings.

The authors acknowledged limitations of the study, including potential misclassification of vaccination or outcomes, inability to verify diagnostic accuracy, limited statistical power for subgroup analyses, and possible residual confounding due to unmeasured behavioural factors.

However, they also noted several key strengths such as the use of comprehensive administrative and delivery registry data within a universal healthcare system, enabling large-scale linkage and near-complete follow-up.

Importance of maternal influenza and Tdap vaccination

It was concluded that the findings supported current recommendations for maternal influenza and Tdap vaccination during pregnancy and highlighted the urgent need to improve vaccine uptake, particularly given persistently suboptimal coverage rates.

A recent clinical consensus statement from the European Society of Cardiology highlights the pivotal role of vaccination in the prevention of major cardiovascular events. It emphasises the link between influenza and acute myocardial infarction, heart failure and other cardiovascular complications.

Professor Thomas Lüscher, ESC president, notes that any patients with heart disease ‘who want to become pregnant should be vaccinated beforehand, and this is recommended by paediatricians as well as the ESC’.

And any woman who becomes pregnant should be vaccinated ‘at the earliest opportunity’ for their own protection but also that of their baby, he adds.

Reference
Morabito G. Maternal Vaccine Receipt and Infant Hospital and Emergency Visits for Influenza and Pertussis. JAMA Netw Open 2026;9(1):e2553179.