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Infant, maternal and demographic predictors of delayed vaccination: A population-based cohort study
Heather F Gidding1, Lloyd K Flack2, Sarah Sheridan1
1Women and Babies Research, Kolling Institute, Northern Sydney Local Health District, St Leonards, NSW, Australia; The University of Sydney Northern Clinical School, NSW, Australia; National Centre for Immunisation Research and Surveillance of Vaccine Preventable Diseases, Sydney, NSW, Australia; School of Public Health and Community Medicine, UNSW Medicine, University of NSW, Sydney, NSW, Australia.
Insights
Delayed infant vaccination, particularly the first dose of diphtheria-tetanus-pertussis (DTP1), is more common in Aboriginal children and linked to maternal factors. Improving DTP1 timeliness significantly reduces delays in subsequent DTP doses.
Area of Science:
- Public Health
- Immunization Programs
- Child Health
Background:
- Vaccination timeliness is a critical measure of immunization program performance.
- Limited research exists on comprehensive predictors of delayed infant vaccination.
- This study addresses the gap by examining factors influencing diphtheria-tetanus-pertussis (DTP) vaccination delays.
Purpose of the Study:
- To identify predictors of short and longer-term delays in DTP vaccination.
- To analyze these predictors by vaccine dose number and ethnicity.
- To inform strategies for improving infant immunization timeliness.
Main Methods:
- Linked perinatal, notification, death, and immunization databases for 1.3 million births (2000-2011) in Australia.
- Used ordinal logistic regression to analyze adjusted relative risks (RR) for vaccination delays.
- Separate models were developed for each DTP vaccine dose and for Aboriginal and non-Aboriginal children.
Main Results:
- Delayed DTP vaccination was more prevalent in Aboriginal children (19.4%) compared to non-Aboriginal children (8.1%) for the first dose (DTP1).
- Delayed DTP1 receipt was a significant predictor of subsequent DTP dose delays, increasing risk by 1.6 to 2-fold per week of delay.
- Highest risk factors for DTP1 delay included mothers with ≥3 previous pregnancies (RR ≥5) and mothers <20 years old (RR ≥2).
- Other predictors included prematurity, maternal smoking, and place of birth (Western Australia for Aboriginal children, Oceania region for others).
Conclusions:
- Identified at-risk subpopulations for delayed infant vaccination, applicable to other high-income settings.
- Improving timeliness of the first DTP dose, especially for children with older siblings, can yield substantial benefits for subsequent dose timeliness.
- Targeted interventions for high-risk groups are crucial for enhancing overall childhood immunization coverage and timeliness.
Background:
Receiving vaccines at or close to their due date (vaccination timeliness) is a now key measure of program performance. However, studies comprehensively examining predictors of delayed infant vaccination are lacking. We aimed to identify predictors of short and longer-term delays in diphtheria-tetanus-pertussis (DTP) vaccination by dose number and ethnicity.
Methods:
Perinatal, notification, death and immunisation databases were linked for 1.3 million births in 2000-11 from two Australian states (Western Australia and New South Wales), with follow-up data until 2013. Ordinal logistic regression was used to estimate adjusted relative risks (RR) by degree of delay. Separate models were constructed for each vaccine dose and for Aboriginal and non-Aboriginal children.
Results:
Each dose-specific cohort included at least 49,000 Aboriginal and 1.1 million non-Aboriginal children. Delayed receipt was more common among Aboriginal than non-Aboriginal children (eg for the first dose of DTP [DTP1] 19.4 v 8.1%). Risk factors for delayed vaccination were strongest for DTP1, and delayed receipt of DTP1 was a key driver of subsequent delays; every week DTP1 was delayed was associated with a 1.6 to 2-fold increased risk of delayed DTP2 receipt. For DTP1, ≥3 previous pregnancies (the only factor more strongly associated with longer than shorter delays; RR ≥5 compared to no previous pregnancies), and children born to mothers <20 years of age (RR ≥2 compared to ≥35 years) were at highest risk of delay. Other independent predictors were prematurity, maternal smoking during pregnancy, and being born in Western Australia (if Aboriginal) or another country in the Oceania region.
Conclusion:
The sub-populations at risk for delayed vaccination we have identified are likely generalisable to other high-income settings. Measures to improve their dose 1 timeliness, particularly for children with older siblings, are likely to have significant flow-on benefits for timeliness of later doses.
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