Inching Toward a Serogroup B Meningococcal Vaccine for Infants

In the past decade, the introduction of meningococcal conjugate vaccines has led to substantial reductions in meningococcal disease. Monovalent serogroup C vaccines have virtually eliminated serogroup C disease from the United Kingdom and other countries, and serogroup A, C, W, and Y vaccines have reduced disease among adolescents in the United States.^{1 - 2} In 2010 and 2011, Burkina Faso, Mali, Niger, and part of Nigeria introduced serogroup A conjugate vaccine, which may eliminate epidemic meningitis from the meningitis belt of Africa. These accomplishments have been dampened by the lack of effective serogroup B meningococcal vaccines. Serogroup B meningococcal disease causes substantial morbidity and mortality globally, especially in young infants.^{3 - 5} Serogroup B disease can be devastating; 5% to 10% of children with the disease do not survive and another 10% to 20% experience long-term sequelae such as hearing loss, limb loss, and neurologic deficits.⁵ Disease burden is lower in the United States than in other countries; incidence of serogroup B disease is 0.16 per 100 000 population but 3.08 per 100 000 population among infants younger than 12 months.⁴ In contrast, incidence of serogroup B disease in several countries in Europe, including the United Kingdom, is about 10-fold that in the United States.³

Serogroup B polysaccharide has not been a successful vaccine target because it is similar to human neural cell glycopeptide and therefore poorly immunogenic in humans. For a serogroup B vaccine to have a substantial effect on disease burden, it will need to be immunogenic and safe in young infants, protect against a high proportion of serogroup B strains, and provide long-term protection.

In this issue of JAMA, the report by Gossger and colleagues⁶ represents a major step forward in developing a broadly protective serogroup B vaccine that is safe and immunogenic in young infants. By sequencing the meningococcal B genome and testing surface antigens for their ability to elicit an immunogenic response, 3 novel antigens were identified—factor-H binding protein (fHbp), Neisserial adhesin A (NadA), and Neisseria heparin binding antigen (NHBA)—and combined with outer membrane vesicle (OMV) from the New Zealand epidemic strain NZ98/254 in a multicomponent serogroup B meningococcal vaccine (4CMenB). This innovative technology identified noncapsular antigens that are surface expressed and can produce antibodies that kill the organism.

The primary objective of the study was to assess the immunogenicity and reactogenicity of 4CMenB in 1885 infants who were given the vaccine in 2 different schedules (2, 4, and 6 months and 2, 3, and 4 months) and concomitantly or separately from routine vaccines. The immunologic end point was the percentage of participants with a human complement serum bactericidal activity (hSBA) titer of 5 or greater against 3 meningococcal serogroup B strains, measured 30 days after the third dose of 4CMenB. Three target strains were chosen to determine the immunogenicity against 3 vaccine components (fHbp, NadA, and OMV); each strain chosen expressed 1 target antigen but did not express the other antigens. There was no target strain available for NHBA at the time of the study, so testing using enzyme-linked immunosorbent assay was performed to evaluate response to NHBA. In each of the different vaccination groups receiving 4CMenB, more than 99% of participants had hSBA titers of 1:5 or greater in response to the strains specific for the fHbp and NadA components of the vaccine; 79% to 81.7% of participants had responses to the strain specific for the OMV component, depending on the schedule used.

As the authors indicated, these strains were not chosen to be representative of disease-causing strains, which vary by country. Studies evaluating antigen expression using isolates collected from surveillance suggest that 4CMenB vaccine could be protective against approximately 76% of strains circulating in Europe.⁷ However, because it is not fully understood how the multiple vaccine components will work together in vivo, antigen expression may be an underestimate or overestimate of the proportion of circulating strains that can be killed. Additionally, even though more than 99% of participants had an hSBA titer indicating an immune response against the strains specific for fHbp and NadA 30 days after dose 3, the geometric mean titers (GMTs) against these 2 strains varied from 80 to 110 for strain 44/76-SL (fHbp) to 315 to 669 for strain 5/99 (NadA). High initial GMTs are important for long-term protection, because studies have shown that antibody persistence is important for protection against serogroup C disease.⁸ It is possible that duration of protection will depend on the characteristics of the strains circulating in the country. For example, only 39% of US serogroup B isolates have a NadA gene, so protection may be more dependent on antibody against fHbp⁹ ; GMTs against fHbp were much lower than those against NadA and may fall below protective levels more quickly. In addition, the contribution of NHBA is not well understood. Although antibodies to NHBA have been shown to kill meningococci, it is not clear how much protection would be provided by these antibodies.¹⁰

Important secondary outcomes of this study were noninferiority of immune responses to 4CMenB and routine vaccines administered together compared with separately. The study met prespecified noninferiority criteria for all antigens except pertactin in the pertussis vaccine and serotype 6b in the 7-valent pneumococcal vaccine. Additionally, the group that received 4CMenB vaccine in the month between routine vaccines had higher hSBA GMTs for all 3 strains tested compared with the concomitant and accelerated groups. Although overall the data on interference are reassuring, these subtle findings highlight the complexity of immunologic interference with the use of various combination vaccines and concomitant vaccination.¹¹

The last critical element of a serogroup B vaccine is for the vaccine to be safe and the reactogenicity profile to be tolerable. Although the overall safety profile of the 4CMenB vaccine was similar to that of other routine infant vaccines, the rates of fever were higher. Six children who received 4CMenB vaccine (about 0.4%) were hospitalized for fever following 4CMenB vaccine, and 1 child experienced a febrile seizure. The New Zealand OMV vaccine produced high rates of fever in clinical trials, so the high rates of fever seen with 4CMenB are not surprising.¹² However, these high rates of fever may cause some additional strain on the health system, including additional ambulatory visits and hospitalizations, and may dampen parental acceptance. The fever profile will likely be more acceptable in countries with a higher burden of serogroup B disease.

The results of the study by Gossger et al⁶ demonstrate this serogroup B vaccine is immunogenic in infants; however, there is still much to understand about effective implementation of programs using noncapsular-based meningococcal vaccines. The potential of 4CMenB vaccine to reduce serogroup B meningococcal disease is substantial, but it cannot be compared with the success of conjugate vaccine programs. 4CMenB vaccine may not reduce nasopharyngeal carriage or produce herd immunity, as the serogroup C conjugate vaccine did in the United Kingdom.¹³ Booster doses may be required to sustain protection but may not confer the same degree of immunologic memory as conjugate vaccines.¹⁴ Countries will have to weigh the benefits of serogroup B vaccination against the costs of adding vaccines to the infant schedule. However, the anticipated licensure of this vaccine in Europe and other countries means that for the first time vaccines to prevent all 5 of the serogroups that cause most meningococcal disease worldwide will be available.