Hospitalisation of preterm infants with pertussis in the context of a maternal vaccination programme in England

Aims To assess whether preterm infants are at increased risk of pertussis infection and whether this increased following introduction of a maternal pertussis vaccination in England, while examining characteristics of infants associated with more severe disease. Methods Infants aged <60 days admitted between 1 April 2009 and 31 March 2016 with a pertussis diagnosis code were extracted from Hospital Episode Statistics (HES) data. HES data were reconciled with existing surveillance systems to capture maternal vaccination status where available. Cases were compared preimplementation and postimplementation of the maternal programme with respect to demography, preterm or full-term birth and coinfection. Survival analysis was undertaken to assess the impact of variables on duration of hospital stay. Results The proportion of hospitalised preterm infants (138/1309, 10.6%) was higher than population estimates (7.4%), increasing from 9.8% (83/847) to 12.1% (56/462) following implementation of the maternal programme. Longer duration of hospital stay was associated with prematurity, younger age, additional respiratory illnesses and mothers unvaccinated in pregnancy. Of 13 deaths, 5 were preterm (38.5%) and 11 (84.6%) were female. A larger proportion of full-term infants' (49/188, 26.1%) mothers had been vaccinated in pregnancy than preterm infants (7/49, 14.3%), with 14.3% of mothers of full-term cases vaccinated after 35 weeks. Conclusions Preterm infants are over-represented in hospitalised pertussis cases and have less benefit from the maternal pertussis vaccination programme in England due to reduced opportunity for maternal vaccination.