Quadrivalent Conjugate Vaccine and Invasive Meningococcal Disease in US Adolescents and Young Adults.

Importance: Beginning in 2005, the US implemented routine immunization of adolescents with a quadrivalent conjugate vaccine (MenACWY) for the prevention of invasive meningococcal disease (IMD).

Objectives: To assess whether MenACWY immunization was associated with a reduced IMD burden among the US adolescent population and how the downward trajectory of IMD that began in the mid-1990s might have evolved in the absence of vaccination efforts.

Design, setting, and participants: In this decision analytical study, a bayesian hierarchical Poisson regression model was developed to investigate the potential trajectory of IMD among US adolescents and young adults without vaccination and evaluate the direct association of vaccination with IMD burden. The model included the entire age-stratified US population and was fitted to national incidence data for serogroups C, W, and Y from January 1, 2001, to December 31, 2021, with stratification by vaccination status for IMD cases.

Intervention: Simulated counterfactual scenario of absent vaccination from 2005 to 2021, while retaining the incidence rate of IMD for unvaccinated individuals estimated during model fitting.

Main outcomes and measures: The main outcomes were the estimated numbers of IMD cases and deaths averted by MenACWY vaccination among US adolescents and young adults aged 11 to 23 years.

Results: Among the entire US population from 2005 to 2021, MenACWY vaccination prevented an estimated 172 (95% credible interval [CrI], 85-345) cases of IMD among US adolescents 11 to 15 years of age and 328 (95% CrI, 164-646) cases of IMD among those aged 16 to 23 years. Absent vaccination, the cumulative incidence of IMD in these age groups would have been at least 59% higher than reported over the same period with vaccination. Using case fatality rates of unvaccinated individuals derived from national data, vaccination averted an estimated 16 (95% CrI, 8-31) deaths among adolescents aged 11 to 15 years and 38 (95% CrI, 19-75) deaths among those aged 16 to 23 years.

Conclusions and relevance: This decision analytical model suggests that the MenACWY vaccination program in the US was associated with a reduced burden of meningococcal disease. Without vaccination, the incidence rates per 100 000 adolescents and young adults would have been substantially higher than those observed during the vaccine era.