Infants aged younger than two months had higher rates of morbidity and death related to pertussis in the era of acellular vaccination, according to a study published in the Journal of the Pediatric Infectious Diseases Society.

There is still a significant burden of severe pertussis disease in Canada, despite the success of current vaccines,” Manish Sadarangani, MA, BM, BCh, MRCPCH, DPhil, an assistant professor of pediatric infectious diseases at the University of British Columbia and director of the Vaccine Evaluation Center, BC Children’s Hospital Research Institute, told Infectious Diseases in Children.

Acellular vaccination.

The youngest and most vulnerable children (including premature babies) in our population are at highest risk for the most severe outcomes. Found that the overall incidence of pertussis in the United States increased between 2000 and 2016, with age-specific case counts coinciding with the transition to acellular vaccination.

In that study, researchers wrote that despite substantial declines in the disease since the vaccine was introduced, pertussis incidence increased in several countries in recent years. Sadarangani and colleagues noted that having data on pediatric pertussis using data from a large population over time would help to establish “the true burden of disease for the [acellular pertussis] vaccine era.”

They studied 1,402 patients aged 16 years and younger with pertussis who were admitted to 12 pediatric tertiary care hospitals in Canada between 1999 and 2015. The researchers reported that younger infants those aged younger than two months experienced the highest mean annual incidences of pertussis hospitalization (116.4 per 100,000 population; 95% CI, 85.32-147.49) and ICU admission (33.48 per 100,000 population; 95% CI, 26.35-40.62).

There were 25.46% of children requiring ICU admission, with infants aged younger than two months experiencing the highest proportion of ICU admission, at 37.9%.Sadarangani and colleagues wrote that 21 deaths occurred between 1999 and 2015. Independent risk factors for ICU admission included age younger than 16 weeks, prematurity, encephalopathy and a confirmed diagnosis of pertussis. Independent risk factors for death included age younger than four weeks, prematurity and female sex.

“Pertussis vaccination in pregnancy is now recommended for all pregnant women in Canada in every pregnancy and is the most effective means we have to protect these youngest babies it is now imperative that these immunization programs are implemented across the country,” Sadarangani said. “While we know that pertussis immunization in pregnancy is safe and effective, there are remaining research questions to confirm the best time to vaccinate during pregnancy and increase our understanding of the immunology of immunization in pregnancy.