Estimating the potential number of cases prevented by infant/ toddler immunisation with a MenACWY vaccine

Introduction: Meningococcal disease control in the UK relies on various vaccines, with the discontinuation of the Hib/MenC combination vaccine Menitorix® in 2018 necessitating reassessment of the immunisation strategy. The quadrivalent MenACWY vaccine emerges as a promising long-term solution, already integrated into the teenage immunisation regimen. While indirect control of group W and C cases is anticipated through existing programs, the high incidence of meningococcal disease in infancy underscores the potential benefits of infant/toddler vaccination. Methods: Utilizing data from two UK studies, we recalibrated age-specific carriage prevalence curves and estimated the proportion of meningococcal carriage attributed to ACWY and non-ACWY strains. Employing a dynamic transmission model, we evaluated the combined indirect effects of the teenage MenACWY vaccination initiative and the direct impact of administering MenACWY vaccine at either 3 or 12 months, alongside ongoing 4CMenB vaccination efforts. Given the pandemic-induced decline in cases and alterations in social contact patterns reported in prior research, we also simulated the transmission model to reflect periods of COVID-19 lockdown. Results: Our projections indicate effective control of carriage and disease associated with groups A, C, W, and Y through the teenage vaccination campaign. Assuming sustained high uptake of teenage vaccines amid pandemic scenario, we forecast MenACWY carriage prevalence to be below 1% by 2025. Across all scenarios, the impact of an infant/toddler MenACWY program on case reduction remains modest. Notably, administering the MenACWY dose at 3 months yields a greater number of prevented cases compared to administration at 12 months. With sustained uptake of teenage vaccination, our estimates suggest that between 3 and 22 cases could be averted in a 2025 birth cohort through a 3-month MenACWY dose. Conclusions: Provided teenage uptake remains high and the infant 4CMenB programme is maintained, we suggest that few cases will be prevented from an infant/ toddler MenACWY dose.