Migration and infant immunization timeliness in New Zealand: Evidence from the Growing Up in New Zealand study.

Background: Migration has been recognized as an important determinant of child health outcomes including childhood vaccination status. This paper aims to examine the association between parental migration status and a less studied aspect of child immunization outcomes, namely timeliness, within the context of New Zealand (NZ), a country characterized by a substantial proportion of its resident population born overseas. Additionally, the study explored the impact of residential duration on children's immunization timeliness.

Methods: The data was taken from a large, representative population-based cohort study in NZ (Growing Up in NZ study). A total of 6156 children and their parents, comprising 2241 foreign-born and 3915 NZ-born mothers and a sub-group of their partners were included in the analysis. The survey data was linked with the National Immunization Register dataset. Timely immunization was defined as receiving two vaccines at each scheduled vaccination point (at six-week, three-month, and five-month, totaling six doses of vaccines) within 30 days of their due date. We examined the associations between parental migration status, maternal residential duration, and child immunization timeliness while controlling for socio-economic variations. The results were presented as adjusted odds ratios (AORs) with 95 % confidence intervals (CIs).

Results: The findings revealed that after adjustment for socioeconomic differences, children of foreign-born mothers exhibited higher odds of receiving all six studied vaccine doses on time compared to children of native-born mothers (AOR 1.51, 95 %CI:1.27-1.78). Similarly, having a foreign-born father was also significantly associated with timely completion of all six vaccine doses. Children of recent immigrants who had resided in the country for less than five years demonstrated higher odds of timely vaccination of all six vaccine doses compared to children of settled immigrants who had lived in the country for five or more years (AOR 1.65, 95 %CI: 1.25-2.19).

Conclusion: This study revealed a significant pattern in NZ where immigrants exhibited higher rates of timely immunization for their children compared to native-born parents. However, the findings also underscore the importance of providing support to settled immigrants, as their children experienced declines in timely vaccination rates compared to children of recent immigrants and even those born to NZ-born parents.