No Evidence of Herd Immunity In Pediatric Meningococcal B Vaccine Study

Neisseria meningitidis is a significant cause of meningitis around the world. Meningococcal group B strains cause many cases of invasive meningococcal disease, including approximately one-third of cases in the United States.

The meningococcal group B vaccine 4CMenB, a recombinant protein-based vaccine, has been in use globally since 2014. While previous research has demonstrated the vaccine confers protection individually, a new study published in The New England Journal of Medicine (NEJM) provides evidence that there was no change in herd immunity among more than 34,000 students in Australia with moderate to high vaccination rates.

The investigators of the study used cluster randomization to assign students aged 15 to 18 years to receive 4CMenB vaccination at either baseline (the intervention arm) or at 12 months (control).

The primary outcome was oropharyngeal carriage of N meningitidis group A, B, C, W, X, or Y. Oropharyngeal carriage of N meningitidis was established through polymerase chain reaction assays for N meningitidis genogroups and encoding porin protein A.

From April through June 2017 investigators enrolled 24,269 students in grades 10 and 11, as well as 10,220 students in grade 12. A total of 237 schools in South Australia participated.

At 12 months, the vaccination group had a 2.55% prevalence of N meningitidis, representing 326 of 12,756 students in the group.

In the control group, the prevalence of N meningitidis was 2.52%, representing 291 of 11,523 students, carried N meningitidis.

Notably, there were no cases of meningococcal B disease in the trial population during the study period, compared with 12 cases among students 15 to 18 years of age in the 2015-16 period.

As of December 27, 2019, there were still no cases of meningococcal B disease in the trial population.

"Our study has shown good protection was provided by the meningococcal B vaccine against meningococcal disease in those vaccinated but did not show an overall reduction in the proportion of adolescents carrying the bacteria, including the B strain," said study author Helen Marshall, MD, MPH, DCH, MBBS, a professor at the University of Adelaide, in a press release.

Risk factors for carriage were assessed at baseline. Risk factors included later year of schooling, current upper respiratory tract infection, water-pipe smoking, cigarette smoking, going to pubs or clubs, and reporting 1 or more persons kissed in the past week.

In the same issue of NEJM, a study appeared demonstrating positive effect of 4CMenB against meningococcal group B disease in children in England. But the evidence that herd immunity was not acquired in the Australian study group is important for public health and clinical considerations.

“These results highlight the importance of individual vaccination for adequate protection, as the vaccine is unlikely to be able to stop spread of the bacteria between individuals," Marshall said.