Early estimate of the effectiveness of quadrivalent meningococcal conjugate vaccine.

Background: In January 2005, a quadrivalent meningococcal conjugate vaccine (MenACWYD) was licensed for use in the United States. The Advisory Committee on Immunization Practices recommends MenACWYD for all adolescents 11 to 18 years of age and others at increased risk for meningococcal disease.

Methods: Reports of breakthrough meningococcal disease after vaccination with MenACWYD were collected. A simulation approach was used to estimate the expected number of cases in vaccinated persons.

Results: Between 2005 and 2008, 14 breakthrough cases, including 3 deaths occurred. At a vaccine effectiveness (VE) of 90%, 7 breakthrough cases would be expected (range, 1-17); at VE of 85%, 11 cases (range, 2-30); at VE of 80%, 15 cases (range, 5-28); and at VE of 75%, 18 cases (range, 7-32) would be expected. The probability of the ≥14 observed cases occurring was 2.9% at VE of 90%, 29.3% at VE of 85%, 66.1% at VE of 80%, and 83.0% at VE of 75%.

Conclusions: This report provides an early estimate of MenACWYD effectiveness within 3 to 4 years after vaccination, and suggests that MenACWYD effectiveness is 80% to 85%, similar to the VE reported for meningococcal polysaccharide vaccine.