Importance
Assessing gaps in antenatal pertussis vaccination to increase coverage.

Introduction
Antenatal pertussis vaccination has been proven effective in reducing pertussis disease in infants. Current guidelines recommend maternal pertussis vaccination from 28 weeks gestation. The aim of this study is to determine antenatal pertussis vaccination coverage in the Northern Territory and potential socio‐demographic factors affecting uptake, using validated birth and immunisation data.

Methods
Cross‐sectional population study including all viable births (from 24 weeks gestation) in Northern Territory public hospitals in 2016.

Results
There were 3392 viable delivery episodes in 2016 with 48.9% coverage against maternal pertussis based on current guidelines. Mothers <35 years old were more likely to receive antenatal vaccination (adjusted odds ratio (aOR) = 1.26, CI 1.035–1.52, P = 0.021). Pertussis vaccination coverage for preterm births was low at 0% for extreme, 18.86% for very preterm and 39.8% for moderate preterm births, with an overall coverage of 33.5% for all preterm births. Term births were two times more likely than preterm births to have had mothers receive an antenatal diphtheria toxoid, tetanus toxoid and acellular pertussis vaccine (aOR = 1.957, CI 1.53–2.50, P < 0.001). Conclusions A significant proportion (66.5%) of preterm babies are not benefiting from protection against pertussis with the current pertussis vaccination policy from 28 weeks gestation. As timing of birth cannot be predetermined, a review of safety and acceptability of pertussis vaccine administration in the second trimester is needed. Implementation of pertussis vaccination from 20 weeks gestation will provide a wider vaccination period and maximise the protection of all infants including pre‐term infants from pertussis.