A prospective study of the effectiveness of the New Zealand meningococcal B vaccine.

The effectiveness of a new group B strain-specific meningococcal vaccine referred to as "MeNZB," developed by Chiron Vaccines (Siena, Italy) in collaboration with the Norwegian Institute of Public Health, was assessed in a prospective observational study following a nationwide vaccination program in New Zealand. The vaccination program began in July 2004, and the study uses data from January 2001 to June 2006. A generalized estimating equation model was used to estimate vaccine effectiveness that included potential confounding variables, such as disease progression over time, age, ethnicity, socioeconomic status, seasonality, and geographic region. The model provides strong statistical evidence for a vaccine effect (p < 0.0001), with estimated disease rates 3.7 times higher in the unvaccinated group than in the vaccinated group (95% confidence interval: 2.1, 6.8) and a vaccine effectiveness of 73% (95% confidence interval: 52, 85). An estimated 54 epidemic strain meningococcal cases were prevented in the 2 years since the vaccination program began (95% confidence interval assuming a fixed population size: 22, 115). In a sensitivity analysis, these estimates proved to be robust to modeling assumptions, including population estimates, estimates of the numbers vaccinated, effects of partial vaccination, and temporal autocorrelation.