FROM THE NEW ENGLAND JOURNAL OF MEDICINE

One-third of the individuals who received a multicomponent meningococcal B vaccine during an outbreak did not show a protective response against the outbreak strain, though they also did not contract the disease, a study showed.

“This level of seropositivity was lower than expected, given the antigenic similarity between the outbreak strain and the components of the vaccine and given that the Meningococcal Antigen Typing System predicted that 4CMenB would induce responses against the outbreak strain,” Nicole E. Basta, PhD, of the University of Minnesota, Minneapolis, and her associates wrote in the New England Journal of Medicine ( 2016;375:220-8. doi:10.1056/NEJMoa1514866 ).

“Our results indicate that knowledge of [human complement serum bactericidal antibodies] immunity against the vaccine reference strains is not sufficient to predict individual-level immunity against an outbreak strain, even when the strain expresses one or more antigens that are closely related to the vaccine antigens,” the investigators added.

Amidst an outbreak of meningococcal B at Princeton (N.J.) University in the winter of 2013, the Food and Drug Administration allowed use of the meningococcal serogroup B (4CMenB) vaccine before its licensure, in an attempt to control the outbreak. Two strains of meningitis were used in developing this vaccine: 5/99 strain, which was not at all similar to the outbreak strain, and 44/76-SL, which was 96% genetically similar to the outbreak strain.

Among 535 people who completed the study, 499 individuals received two doses of 4CMenB 10 weeks apart, 17 received one dose of the vaccine, and 19 were unvaccinated. When the fully vaccinated individuals were tested for titers 8 weeks after their second dose, two-thirds (66.1%) had low-level seropositivity for the outbreak strain, with a geometric mean titer (GMT) of 7.6. One in five of the unvaccinated people (21.1%) had low seropositivity for the outbreak strain (GMT, 2.8), and 58.8% of the partly vaccinated individuals had seropositivity with a GMT of 5.4.

The researchers then assessed titers for the two strains used in developing 4CMenB in 61 fully vaccinated individuals, all randomly selected from the one-third of fully vaccinated people who did not have a detectable response to the outbreak strain. Most of them (86.9%) were seropositive for the 44/76-SL strain with a GMT of 17.4, and all of them were seropositive for the 5/99 strain, with a considerably larger GMT of 256.3.

Among those fully vaccinated who responded to the outbreak strain with titers above 8, all had seropositivity for 44/76-SL (GMT, 178.8), and 96.7% had seropositivity for the 5/99 strain (GMT, 214.2). Among the 18 unvaccinated individuals, just 1 had very low seropositivity to the 5/99 strain (GMT, 1.2), and 6 of them (33.3%) responded to the 44/76-SL strain (GMT, 3.2).

“These findings have implications for vaccination policies aimed at preventing and controlling meningococcal B disease,” the authors wrote.

The research was funded by Princeton University, the National Institutes of Health, and the Department of Homeland Security. Dr. Bai, Dr. Borrow, and Dr. Findlow reported having previously received research funding, unrelated to this study, from GlaxoSmithKline, Novartis, Pfizer, and Sanofi Pasteur. Dr. Johnsen has been reimbursed for travel expenses from Pfizer for a presentation. No other authors had financial disclosures.

imnews@frontlinemedcom.com

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