Pertussis Disease and Antenatal Vaccine Effectiveness in Australian Children

Abstract

Background: Population-level studies of severe pertussis extending beyond infancy are sparse, and none in the context of antenatal vaccination. We compared hospitalized pertussis cases from birth to 15 years of age before and after introduction of antenatal immunization. Methods: Active surveillance of laboratory-confirmed pertussis hospitalizations in a national network of pediatric hospitals in Australia January 2012 to June 2019. Impact of maternal vaccination was assessed by vaccine effectiveness (VE) in cases and test-negative controls with <2 months of age and by before-after comparison of age distribution of cases. Among cases eligible for one or more vaccine doses, we examined proportions ageappropriately immunized and with comorbidities by age group. Results: Among 419 eligible cases, the proportion <2 months of age significantly decreased from 33.1% in 2012 to 2014 compared with 19.6% in 2016 to 2019 when mothers of only 4 of 17 (23.5%) cases <2 months of age had received antenatal vaccination. VE was estimated to be 84.3% (95% CI, 26.1-96.7). Across all years (2012-2019), of 55 cases 4-11 months of age, 21 (38%) had ≥2 vaccine doses, whereas among 155 cases ≥12 months of age, 122 (85.2%) had ≥3 vaccine doses. Prevalence of comorbidities (primarily cardiorespiratory) increased from 5 (2.1%) <6 months of age to 36 (24.2%) ≥12 months of age (P < 0.001), with 6/16 (38%) cases ≥12 months of age who required intensive care having comorbidities.Conclusions: Below the age of 12 months, prevention of severe pertussis will be maximized by high maternal antenatal vaccine uptake and timeliness of infant vaccine doses. Despite full immunization, we found children ≥12 months of age accounted for 27% of hospitalizations <15 years, with 24% having comorbities, suggesting new vaccine strategies, such as additional doses or more immunogenic vaccines, require evaluation.

Maternal pertussis immunization and the blunting of routine vaccine effectiveness: A meta-analysis and modeling study

“…Unvaccinated newborns are the age group most vulnerable to pertussis, both in terms of infection and hospitalization risks 6,7,8 . Our study suggests that, although blunting may erode the benefits of immunization in infants, maternal immunization is highly effective at protecting unvaccinated newborns.…”

“…In 2015, the World Health Organization (WHO) issued an official recommendation for maternal immunization with acellular vaccines against pertussis (based on studies with acellular primary immunization) 9 , and by 2020 maternal immunization against pertussis was recommended in 55 countries 10 . Maternal immunization is highly effective at protecting newborns, with estimates of reductions in the risk of pertussis infection ranging from 70 to 95% 8,[11][12][13][14][15][16][17] . However, the downstream consequences of maternal immunization, when infants receive their routine pertussis vaccines, are poorly understood.…”

The effectiveness of maternal pertussis vaccination for protecting Aboriginal and Torres Strait Islander infants against infection, 2012–2017: a retrospective cohort study

“…During 1997–2014 (ie, prior to the introduction of maternal pertussis vaccination programs), rates of notified pertussis infection, hospitalisation, intensive care unit admission, and death were three to eight times as high for Aboriginal and Torres Strait Islander infants and children under five years of age as for non‐Indigenous infants and children 10,11 . Australian studies of the effectiveness of maternal vaccination for preventing pertussis infections in their infants 12,13 have not taken Indigenous status into account, were not large enough to provide robust estimates for Indigenous infants, and did not undertake time‐varying statistical analyses.…”

Influenza and pertussis vaccine coverage in pregnancy in Australia, 2016–2021

“…Pertussis infection in young infants, while less prevalent compared with influenza, 1 poses a severe threat to those aged < 4 months who have not yet derived protection from their primary vaccination course 12 . Infants aged < 6 months are too young to be vaccinated against influenza and can only be partially immunised against pertussis infections; protection is best mediated via passive maternal transplacental antibody transfer 7,13‐16 …”

“…12 Infants aged < 6 months are too young to be vaccinated against influenza and can only be partially immunised against pertussis infections; protection is best mediated via passive maternal transplacental antibody transfer. 7,[13][14][15][16] Seasonal influenza vaccination in pregnancy (maternal vaccination) has been recommended in Australia since 2000 and the vaccine has been funded for all pregnant women on the National Immunisation Program (NIP) since 2010. 17 Pertussiscontaining vaccines, which also include diphtheria and tetanus antigens, have been recommended in pregnancy since 2013 for women in their third trimester.…”