Investigation of a pertussis outbreak and comparison of two acellular booster pertussis vaccines in a junior school in South East England, 2019.

In March 2019, a pertussis outbreak occurred in children in a junior school (7-11 years) in England who had been offered pertussis-containing booster vaccine at 40 months of age. In a case-control investigation, we assessed the extent of transmission and any difference in protection afforded to those who had previously received a booster 3- or 5-component acellular pertussis vaccine (aP). We took oral fluid specimens from the students to determine IgG antibodies against pertussis toxin (anti-PT). Parents of students attending the school were sent a questionnaire on pertussis symptoms and vaccination status was retrieved from general practitioner records for all students. Of 381 students, 134 (35.2%) were classified as pertussis cases, 133 by demonstration of significant anti-PT IgG titres and one clinically. There was no significant difference in the risk of pertussis between students receiving 3-component (33.7%) or 5-component (32.3%) aP boosters. However, pertussis infection differed significantly in school year 4, with 22.9%, 50.0%, 23.7% and 38.1% pertussis cases in years 3, 4, 5 and 6, respectively. The proportion of students with incomplete vaccinations recorded was higher than the proportion of those not covered according to the national reported coverage, possibly contributing to sustained transmission within the school.