Long-term 4CMenB Vaccine Effectiveness Against Gonococcal Infection at Four Years Post-Program Implementation: Observational Case-Control Study.

Background: A 4-component meningococcal B (4CMenB) vaccine program was introduced in adolescents in 2019 in South Australia. We aimed to evaluate long-term vaccine effectiveness (VE) and impact (VI) on gonococcal infection 4 years after implementation of the program. Methods: Disease notification data were provided by SA Health. VE was estimated as the reduction in the odds of infection using the screening and case-control methods. Time-to-event analyses assessed vaccine effect on reinfections. VI was estimated as incidence rate ratios (IRRs) using negative binomial regression models. Results: At 4 years after implementation of the program, 2-dose VE against gonococcal infection was 44.3% (95% CI, 35.1%-52.2%) using chlamydia patients as controls. Lower VE estimates were demonstrated in those >48 months post-4CMenB vaccination (26.2%; 95% CI, -2.6% to 47.0%) compared with those who had been vaccinated within ≤48 months (46.0%; 95% CI, 36.3%-54.2%). Slightly higher VE estimates were observed in females (48.7%; 95% CI, 36.9%-58.2%) compared with males (38.0%; 95% CI, 22.0%-50.7%). The risk of a second episode of gonococcal infection was lower in vaccinated gonococcal cases (adjusted hazard ratio, 0.682; 95% CI, 0.450-1.034). The adjusted IRR was 0.635 (95% CI, 0.421-0.957), with an observed 36.5% reduction in gonococcal infection. Conclusions: 4CMenB demonstrates moderate effectiveness against gonococcal infection, with a lower VE estimate after 4 years postvaccination. 4CMenB may reduce the risk of recurrent gonococcal infection. The requirement for a booster dose and dosing interval warrants evaluation.