To evaluate persistence of vaccine effectiveness (VE) and vaccine impact (VI) on invasive meningococcal B (MenB) disease and gonorrhoea at three years after implementation of a state funded 4CMenB programme for infants, children, adolescents and young people in South Australia.

VI was assessed using a Poisson or negative binomial regression model, and VE was estimated using screening and case-control methods. Chlamydia controls were used to estimate VE in the primary analysis to control potential confounding effects such as high-risk sexual behaviour associated with sexually transmitted infections.

During the three-year programme, reductions of 63.1% (95%CI 29.0–80.9%) and 78.5% (95%CI 33.0–93.1%) in incidence of MenB disease were observed in infants and adolescents, respectively. There were no cases in infants who had received three doses of 4CMenB. Two-dose VE against MenB disease was 90.7% (95%CI 6.9–99.1%) for the childhood programme and 83.5% (95%CI 0–98.2%) for the adolescent programme. Two-dose VE against gonorrhoea in adolescents was 33.2% (95%CI 15.9–47.0%). Lower VE estimates were demonstrated after 36 months post-vaccination (23.2% (95%CI 0–47.5%)> 36 months post-vaccination compared to 34.9% (95%CI 15.0–50.1%) within 6–36 months). Higher VE estimates were found after excluding patients with repeat gonorrhoea infections (37.3%, 95%CI 19.8–51.0%). For gonorrhoea cases co-infected with chlamydia VE was maintained (44.7% (95%CI 17.1–63.1%).

The third-year evaluation results show persistent vaccine effectiveness of 4CMenB against MenB disease in infants and adolescents. As this is the first ongoing programme for adolescents, moderate vaccine protection against gonorrhoea with waning effectiveness three years post-vaccination was demonstrated in adolescents and young adults. The additional protection of 4CMenB vaccine against gonorrhoea, likely through cross-protection should be considered in cost-effectiveness analyses. A booster dose may need to be further evaluated and considered in adolescents due to waning protection against gonorrhoea demonstrated after 36 months post-vaccination.