Babies with Older Siblings Face Higher Infection Risks and Lower Maternal Vaccination Protection
A new study identifies a concerning pattern: babies with older siblings face higher infection risks while their mothers are less likely to receive recommended vaccinations during later pregnancies. Expanding accessible immunization services is critical to ensuring better protection for these newborns against preventable illnesses.
Highlights
- •Later-born babies have a higher risk of infection due to older siblings bringing pathogens home.
- •Maternal vaccination uptake drops significantly in successive pregnancies, reducing protection for newborns.
- •Data shows a clear decline from first to fourth pregnancies for both pertussis and influenza vaccines.
- •Improving access to vaccination services in pharmacies and community settings is vital for protecting infants.
New research has highlighted a critical health concern for families: babies with older siblings face a higher risk of infection, yet they are significantly less protected through maternal vaccination. This discovery suggests that while older children often introduce illnesses into the home, the level of protective immunity provided to later-born infants via their mothers is declining across successive pregnancies.
The study, which examined data in Aotearoa New Zealand, shows that immunity derived from maternal immunisation during pregnancy is a key defense for newborns. Vaccines administered to expectant mothers help transfer antibodies that shield babies from serious illnesses such as pertussis (whooping cough) and influenza during their most vulnerable months. However, the data reveals a persistent trend where vaccination rates drop as a woman undergoes subsequent pregnancies.
Declining Vaccination Rates and Infection Risks
Analysis of births through June 2025 indicated that while 61% of mothers received a pertussis vaccine and 40% received an influenza vaccine, these numbers fluctuate based on birth order. Specifically, first-time pregnancies showed higher uptake rates of 69% for pertussis and 45% for influenza. By the time a mother reaches her fourth pregnancy, these figures plummet to just 38% and 24%, respectively.
This decline in maternal vaccination creates a dual disadvantage for later-born children. These infants are not only more exposed to pathogens brought home by older siblings—who frequently encounter bugs at school or daycare—but they also enter the world with less passive protection from their mothers. The study confirmed that this birth-order pattern is evident even within the same families, as mothers are statistically less likely to seek immunization in later pregnancies compared to their first.
Improving Access to Preventative Healthcare
The research suggests that the hurdles faced by parents in later pregnancies, such as time constraints and the difficulty of balancing care for multiple children, may contribute to these lower vaccination rates. Experts indicate that public health services need to adapt to support these busy families. Strategies such as expanding access to vaccines through community settings like pharmacies and working closely with midwives have shown promise in increasing coverage.
By making immunisation more convenient, health authorities can better protect the most vulnerable infants. Enhancing awareness and removing logistical barriers are essential steps to ensure that later-born children receive the same level of preventative care as their older siblings. Addressing this "birth-order gap" remains a priority for reducing hospitalizations for respiratory and contagious diseases among newborns.
