Outcomes of meningococcal serogroup B disease in children after implementation of routine infant 4CMenB vaccination in England: an active, prospective, national surveillance study.

Background: In 2015, the UK included 4CMenB, a multi-component, recombinant protein-based vaccine against meningococcal serogroup B (MenB) disease, in the national infant immunisation programme. We aimed to assess the effect of 4CMenB vaccination on the severity of MenB disease presentation and outcomes.

Methods: In this active, prospective, national surveillance study, we used data from the UK Health Security Agency national surveillance of meningococcal disease. We included data from follow-up of children younger than 5 years with laboratory-confirmed MenB disease who were eligible for 4CMenB vaccination with general practice 3-6 months after disease onset. All invasive MenB isolates were tested using the Meningococcal Antigen Typing System to determine whether the isolate was potentially preventable by 4CMenB. Admission to intensive care, death, and, when possible, reported sequelae in survivors were reviewed alongside vaccine status. For the epidemiological analysis, we compared laboratory-confirmed MenB disease cases before 4CMenB implementation (Sept 1, 2010, to March 31, 2015) with those after implementation (Sept 1, 2015, to March 31, 2020). For clinical follow-up and outcomes, we included all children younger than 5 years with laboratory-confirmed MenB disease between Sept 1, 2015, and March 31, 2021.

Findings: Between Sept 1, 2015, and March 31, 2021, there were 371 cases of MenB disease in children younger than 5 years, including 256 (69%) in those younger than 1 year and 128 (35%) in those younger than 3 months. After the introduction of 4CMenB, the peak age of patients with MenB disease shifted from 5-6 months to 1-3 months. Overall, 108 (29%) of 371 children were too young for vaccination, unvaccinated, or developed MenB disease within 14 days of the first dose. Of 110 meningococcal strains characterised, 11 (92%) of 12 were potentially preventable by 4CMenB in unvaccinated children compared with 53 (66%) of 80 in partly vaccinated and 11 (69%) of 16 in fully vaccinated children. 78 (21%) of 371 children required intensive care, and the case fatality ratio was 5% (17 of 371), with 11 of 17 deaths occurring before 1 year of age, including seven in infants who were too young (<8 weeks) for vaccination. Of 354 survivors, 57 (16%) had 74 sequelae reported; 45 (61%) of 74 were neurological, 17 (23%) were physical, two (3%) were behavioural or psychological, and ten (14%) were other complications. Prevalence of sequelae was similar in unvaccinated (15 [15%] of 98) and vaccinated (42 [16%] 256) children, as were composite outcomes of death or sequelae, and intensive care or death or sequelae.

Interpretation: Cases of MenB disease in vaccine-eligible children declined after 4CMenB implementation, but morbidity in vaccinated and unvaccinated children remained unchanged, highlighting the importance of vaccination to prevent MenB disease. The lower peak age of infants with MenB disease after 4CMenB implementation, with a higher case fatality ratio in young infants, highlights the importance of timely vaccination.

Funding: UK Health Security Agency.