Objective: to assess the effectiveness and impact in children vaccinated with Bexero® of the administration of the vaccine in the first ten months following its inclusion in the national immunisation programme.
Design: analytical observational nationwide study of simultaneous cohorts with a prospective cohort and a retrospective cohort.
Setting: Public Health England (PHE) provided epidemiological data on vaccination and cases of meningococcal B (MenB) disease in children in England.
Study population: the vaccine was offered to infants born in July 2015 and after at ages 2 and 4 months, and to infants aged 3 and 4 months born in May and June of 2015. Cohorts were defined based on whether the children had received one or two doses of the vaccine. Children that developed disease after the first dose were excluded from the second dose. Doses were discounted if MenB disease was diagnosed within 14 days of vaccination, and children diagnosed after the second dose were considered to have received a single dose in the analysis. The unexposed cohort consisted of children of the same age during the same months in the four years preceding the study.
Risk factor assessment: the study observed the number of cases of MenB disease diagnosed in the vaccinated cohort over a ten-month period; the data were collected by the PHE national surveillance system.
Outcome assessment: vaccine effectiveness was assessed using the screening method, comparing the proportion of MenB disease cases detected by means of a meningococcal antigen typing system (MATS) with the proportion of vaccinated children in the total vaccine-eligible population (vaccine coverage). The authors also analysed the number of cases of MenB diagnosed during this period in children aged less than 5 years (excluding the vaccinated cohort) (incidence rate ratio in vaccine-eligible children) and compared it with the cases in the equivalent cohorts in the four previous years (incidence rate ratio in vaccine-ineligible children) by means of a Poisson regression model adjusted for changes in disease trends. A time series model was fitted to estimate the incidence of MenB disease in the period under study and for comparison with the actual number of cases. The authors used the incidence rate ratio (IRR) and assessed the impact of the vaccine by means of the relative incidence rate ratio (RIRR).
Main results: the two-dose vaccine effectiveness was high, of 82.9% (95 CI: 24.1 to 95.2) against all MenB strains and 94.4% for vaccine-covered strains. In the ten months of followup, the incidence of MenB dropped by half in vaccinated children compared to the incidence predicted based on previous cohorts (IRR: 0.50; 95 CI: 0.36 to 0.71) (37 versus 74 cases), with a relative reduction of 42% attributable to vaccination (RIRR: 0.58; 95 CI: 0.40 to 0.85). In children aged less than 5 years, there was a 14% reduction in MenB cases in this period compared to previous cohorts (IRR: 0.86; 95 CI: 0.73 to 1.01), but it was not statistically significant (P = .07). The time series model of disease trends showed a 36% reduction in cases attributable to vaccination relative to the predicted incidence (RIRR: 0.64; 95 CI: 0.45 to 0.92).
Conclusion: in children in the United Kingdom, a two-dose 4CMenB (Bexero®) priming schedule was highly effective in preventing meningococcal B disease.
Conflicts of interest: two of the authors disclosed doing contract research for pharmaceutical companies (including GSK), but receiving no personal remuneration.
Funding source: Public Health England, which is part of the Department of Health in the United Kingdom.