Babies facing greater infection exposure receive less maternal protection
In Aotearoa New Zealand, a quiet inequity has emerged within the walls of family life: the babies most exposed to infection — those with older siblings circulating illness through the household — are the least likely to have received the antibody protection that maternal vaccination provides. Research tracking births across nearly a decade reveals that vaccination uptake falls sharply with each successive pregnancy, not merely across different families but within the same mother's own reproductive history. This is not a story of neglect but of accumulating pressure — the ordinary mathematics of a growing family, where time and attention are finite, and where the youngest child inherits both the richest household and its greatest vulnerabilities.
- Later-born babies face a compounding threat: older siblings import respiratory infections into the home precisely when younger children's immune systems are least equipped to resist them.
- Maternal vaccination rates collapse across birth order — pertussis protection drops from 69% in first pregnancies to 38% by the fourth, leaving the most exposed infants with the least antibody defence.
- The pattern holds even within individual women's own pregnancies, suggesting that family growth itself erodes the conditions that support preventive health behaviour.
- Higher hospitalisation rates for pertussis and influenza among later-born New Zealand children confirm that this statistical gap carries real clinical consequence.
- Expanded access through pharmacies and community midwives has already shown it can lift uptake — particularly among Māori women — pointing toward a practical path forward for families most stretched for time.
Any parent who has watched a school-age child bring home a cough knows what follows: the illness moves through the household, finding its most vulnerable target in the youngest. For babies with older siblings, this domestic transmission is not merely inconvenient — it is a genuine health risk during the months when their immune systems are still forming. Maternal vaccination during pregnancy offers a critical buffer, passing antibodies to the infant before birth. Yet new New Zealand research reveals that the babies who need this protection most are the least likely to receive it.
The numbers are unambiguous. Among first pregnancies, 69 percent of mothers received pertussis vaccination and 45 percent received influenza protection. By the fourth pregnancy, those figures had fallen to 38 percent and 24 percent respectively. Crucially, this decline is not simply a difference between families — it persists when tracking the same woman across her own pregnancies. The pattern echoes broader findings: later-born children are breastfed less, attend fewer health checks, and receive fewer childhood immunisations. As families grow, the conditions that support preventive care quietly erode.
The consequences are measurable. New Zealand data confirms that later-born babies are hospitalised more often for pertussis and influenza than their older siblings were at the same age — a double disadvantage in which greater household exposure coincides with reduced maternal antibody protection. The reasons are likely mundane rather than indifferent: time is scarcer, competing demands are greater, and pregnancy care receives less focus when parents are already managing a household of children.
These same pressures, however, point toward workable solutions. New Zealand has begun delivering maternal vaccines through pharmacies and community midwives, and evidence suggests this expansion has already increased uptake, particularly among Māori women. The infrastructure to reach stretched families exists. The remaining task is ensuring it finds those families — especially in later pregnancies — before the gap between risk and protection widens further.
Any parent who has watched a child bring home a cough from school or daycare knows what comes next: the infection spreads through the house like water finding cracks. For babies with older siblings, this domestic transmission becomes a serious health risk during the months when their immune systems are still forming. Maternal vaccination during pregnancy offers a crucial buffer—antibodies passed from mother to child provide real protection against diseases like pertussis and influenza. Yet new research from New Zealand reveals a troubling pattern: the babies who need this protection most are the least likely to receive it.
The mismatch is stark. Vaccination against whooping cough and flu is publicly funded and recommended for every pregnancy in Aotearoa New Zealand, and the evidence is clear that these vaccines reduce hospitalisation and serious illness in infants. But uptake follows a birth-order cliff. Among first pregnancies, 69 percent of mothers received a pertussis vaccine and 45 percent received influenza protection. By the fourth pregnancy, those numbers had collapsed to 38 percent and 24 percent respectively. Data from the Aotearoa Immunisation Register covering births in the year to June 2025 shows the overall picture: 61 percent of mothers received pertussis vaccination and 40 percent received flu vaccination. These aggregate figures obscure what happens within individual families.
Research examining births from 2015 to 2023 reveals that the same mother is less likely to be vaccinated in her later pregnancies than in her earlier ones. Part of this reflects differences between families—mothers who have more children tend to have lower vaccination uptake overall. But the pattern persists even when looking at individual women across their own pregnancies. This finding aligns with broader research showing that parental health decisions shift with birth order. Later-born children are breastfed less frequently, attend fewer health checks, receive fewer childhood immunisations, and their mothers use prenatal care less often.
Meanwhile, the infection risk for later-born babies is genuinely higher. Older siblings bring home respiratory viruses and contagious illnesses, exposing younger children during the critical early months when they are most vulnerable. Studies from other countries have documented higher hospitalisation rates for respiratory conditions in later-born children and more prescriptions for infectious diseases in infancy. New Zealand data confirms this pattern holds for the two diseases targeted by maternal vaccination: pertussis and influenza. Later-born babies end up hospitalised more often for these conditions than their older siblings were at the same age.
The result is a double disadvantage. Babies facing greater infection exposure from household transmission are simultaneously less likely to have received maternal antibody protection. The reasons for declining vaccination uptake across pregnancies are likely multiple. As families grow, parents have less time and attention to divide among competing demands. Pregnancy care and infant health may receive less focus when parents are already managing older children. Parents also learn and adapt as they gain experience, sometimes changing how they approach pregnancy and early childhood care—not always for the better.
These explanations point toward solutions. Research in New Zealand has identified specific barriers to maternal immunisation: gaps in awareness, time constraints, and difficulty accessing services. These obstacles intensify in later pregnancies when parents are already stretched. The country has begun expanding where vaccines can be delivered—pharmacies and community midwives now offer maternal immunisation, and evidence shows this approach has increased uptake, particularly among Māori women. Making vaccination easier to access for busy families, especially those in later pregnancies, could protect the infants currently facing the highest risk. The infrastructure exists. What remains is ensuring it reaches the families who need it most.
Citas Notables
Babies with older siblings face a greater risk of infection, while their mothers are less likely to receive recommended vaccinations during pregnancy— Research findings on birth-order vaccination patterns
La Conversación del Hearth Otra perspectiva de la historia
Why does vaccination uptake fall so sharply with each pregnancy? Is it just that parents get tired?
It's more complex than fatigue, though that's part of it. Parents are dividing time and resources among more children. But the research also shows the same mother is less likely to get vaccinated in her fourth pregnancy than her first—even though she knows more about health by then. It suggests something shifts in how parents prioritize their own care as families grow.
And the babies who miss out—they're actually at higher risk of catching these diseases?
Yes. Older siblings bring infections home from school and childcare. So later-born babies face more exposure to pertussis and influenza during the months when their immune systems are weakest. The data shows they're hospitalised more often for these diseases.
That seems backwards. You'd think parents would be more cautious with later children, not less.
You might expect that. But the pattern is consistent across multiple health behaviours—breastfeeding rates drop, health check attendance drops, childhood immunisations drop. It's not about parental care declining. It's about resources and attention being stretched thinner.
What would actually change this?
Making vaccination easier. Pharmacies and community midwives can deliver these vaccines without parents having to navigate the traditional healthcare system. The evidence from New Zealand shows it works, especially for Māori women. If you remove the friction—the time, the appointments, the barriers—uptake improves.
So this isn't a knowledge problem. Parents know they should be vaccinated.
Exactly. It's a systems problem. Parents aren't choosing not to protect their babies. They're navigating competing demands with limited time and access. Fix the access, and you fix the outcome.