Conference Coverage

No teen herd immunity for 4CMenB in landmark trial


 

REPORTING FROM ESPID 2019

– The 4CMenB vaccine didn’t affect carriage of disease-causing genogroups of Neisseria meningitidis in adolescents in the landmark Australian cluster-randomized trial of herd immunity known as the “B Part of It” study, Helen S. Marshall, MD, reported at the annual meeting of the European Society for Paediatric Infectious Diseases.

This was the largest-ever randomized trial of adolescents vaccinated against meningococcal disease, and the message, albeit somewhat disappointing, is clear: “MenB [Meningococcal serogroup B] vaccine programs should be designed to provide direct protection for those at highest risk of disease,” declared Dr. Marshall, professor of vaccinology and deputy director of the Robinson Research Institute at the University of Adelaide.

In other words, a protein antigen–based MenB vaccine doesn’t provide indirect protection to unvaccinated adolescents through herd immunity. Youths in the age groups at highest risk of disease – infants and adolescents– need to routinely receive the vaccine.

The B Part of It study, whose sheer scope and rigor drew the attention of infectious disease clinical trialists the world over, randomized nearly 35,000 students at all high schools in the state of South Australia– whether urban, rural, or remote– to two doses of the 4CMenB vaccine known as Bexsero or to a nonvaccinated control group. This massive trial entailed training more than 250 nurses in the study procedures and involved 3,100 miles of travel to transport oropharyngeal swab samples obtained from students in outlying areas for centralized laboratory analysis using real-time polymerase chain reaction with meningococcal genotyping, culture for N. meningitidis, and whole-genome sequencing. Samples were obtained on day 1 of the study and 12 months later.

The investigators created widespread regional enthusiasm for this project through adept use of social media and other methods. As a result, 99.5% of students randomized to the intervention arm received one dose, while 97% got two doses. A gratifying unintended consequence of the study was that parents who’d never previously vaccinated their children enrolled them in B Part of It, Dr. Marshall noted.

The impetus for B Part of It was that, while the Australian national health insurance program covers a single dose of meningococcal conjugate MenACWY vaccine given at age 12 months and 14-19 years, MenB vaccine isn’t covered because of uncertainties about cost effectiveness and the vaccine’s impact on meningococcal carriage and herd immunity. B Part of It was designed to resolve those uncertainties.

South Australia has the highest rate of invasive meningococcal disease in the country, and more than 80% of cases there are caused by meningococcal serogroup B. Moreover, 75% of group B cases in South Australia involve the nasty hypervirulent New Zealand strain known as CC 41/44.

The primary outcome in B Part of It was the difference in carriage of the major disease-causing serotypes– groups A, B, C, W, X, and Y– between vaccinated and unvaccinated students at the 1-year follow-up mark. The carriage prevalence of all N. meningitidis in the vaccinated students went from 2.8% at baseline to 4.0% at 12 months, and similarly from 2.6% to 4.7% in unvaccinated controls. More importantly, the prevalence of disease-causing genotypes rose from 1.3% at baseline to 2.4% at follow-up in the vaccinated subjects, with a near-identical pattern seen in controls, where the prevalence rose from 1.4% to 2.4%. In an as-treated analysis, the rate of acquisition of carriage of disease-causing genotypes was identical at 2.0% in both study arms.

The 4CMenB vaccine proved reassuringly safe and effective in preventing meningococcal disease in vaccinated teens. With more than 58,000 doses of the vaccine given in the study, no new safety concerns or signals emerged. And the observed number of cases of invasive meningococcal disease in South Australian adolescent vaccine recipients to date has been significantly lower than expected.

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