Meningococcal Disease in US Military Personnel before and after Adoption of Conjugate Vaccine

To the Editor: In their recent letter (1), Broderick et al. provided useful information about the remarkable declines in incidence of meningococcal disease among active-duty US military personnel since the early 1970s, when meningococcal vaccination began within that population. The authors reported that the incidence of meningococcal disease from vaccine-covered serogroups was 0.183 cases/100,000 persons during 2006–2013 among persons vaccinated with quadrivalent conjugate meningococcal vaccine (MCV-4), compared with 0.307 cases/100,000 persons during 2000–2013 among persons vaccinated with quadrivalent polysaccharide meningococcal vaccine (MPSV-4). They stated that, because these rates did not differ significantly, case rates were similar in personnel vaccinated with MCV-4 and MPSV-4. Although statistically correct, this comment might mislead the unwary reader.

The absence of a significant difference does not necessarily mean that the 2 vaccines have similar effectiveness. The incidence rate of meningococcal disease was 68% higher ([0.307–0.183] × 100/0.183) during the period of MPSV-4 use than during the period of MCV-4 use. If the same findings arose in a study of sufficient size to achieve statistical significance, this difference would be considered of substantial clinical importance. A happy consequence of the long-term temporal trends in meningococcal incidence and the success of these vaccines is that the incidence of meningococcal disease is now sufficiently reduced that even the very large active-duty population is too small to provide the statistical power to declare these 2 different incidence rates as being statistically different.

The trends reported by Broderick et al. have continued. During 2006–2014, the incidence of meningococcal disease caused by vaccine-covered serogroups among US military recipients of MCV-4 fell to 0.146 per 100,000 person-years, whereas MPVS-4–related incidence did not change (M.P. Broderick, pers. comm.). Furthermore, through July 2016, the US military has not seen a case from a covered serogroup since 2011 among recipients of MCV-4. Even with these additional data, however, the difference between MCV-4 and MPSV-4 does not achieve statistical significance (M.P. Broderick, pers. comm.).

Michael D. Decker

Author affiliation: Sanofi Pasteur, Swiftwater, Pennsylvania, USA; Vanderbilt University School of Medicine, Nashville, Tennessee, USA

Acknowledgment

The author is an employee of a company that manufactures both conjugate and polysaccharide meningococcal vaccines.

References

Broderick MP, Phillips C, Faix D. Meningococcal disease in US military personnel before and after adoption of conjugate vaccine. Emerg Infect Dis. 2015;21:377–9.DOI PubMed

Suggested citation for this article: Decker MD. Meningococcal disease in US military personnel before and after adoption of conjugate vaccine [letter]. Emerg Infect Dis. 2016 Nov [date cited]. http://dx.doi.org/10.3201/eid2211.150498

DOI: 10.3201/eid2211.150498