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Objectives: 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., Methods: 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., Results: 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%)., Conclusion: 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., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Helen Marshall is an investigator on vaccine trials sponsored by iILiAD Biotechnologies, Pfizer, and Sanofi. Helen Marshall’s, Bing Wang’s, Prabha Andraweera's and Mark McMillan's institution receives funding for investigator-led studies from industry, including GSK, Pfizer and Sanofi Pasteur; Helen Marshall, Bing Wang, Prabha Andraweera and Mark McMillan receive no personal payments from industry. All other authors report no potential conflicts of interest., (Copyright © 2023 The British Infection Association. All rights reserved.)

Background: A programme of vaccination with the four-component serogroup B meningococcal (4CMenB) vaccine was introduced in South Australia for infants and children aged 0-3 years on Oct 1, 2018, and for senior school students in school years 10 and 11 (aged 15-16 years) and young adults aged 17-20 years on Feb 1, 2019. We aimed to evaluate vaccine effectiveness and impact on serogroup B meningococcal disease and gonorrhoea 2 years after implementation of the programme., Methods: We did a cohort and case-control study among those targeted by the South Australia 4CMenB vaccination programme. We obtained disease notification data from SA Health, Government of South Australia, and vaccine coverage data from the South Australian records of the Australian Immunisation Register. Vaccine effectiveness was estimated as the reduction in the odds of infection using the screening and case-control methods. Vaccine impact was estimated as incidence rate ratios (IRRs), obtained by comparing case numbers in each year following the start of the vaccination programme with cases in the equivalent age cohort during the pre-vaccination programme years. We used Poisson or negative binomial models, as appropriate, with adjustment for changes in the incidence of serogroup B meningococcal disease in age cohorts not eligible for vaccination through the state programme., Findings: 4CMenB vaccine coverage 2 years after introduction of the childhood vaccination programme was 94·9% (33 357 of 35 144 eligible individuals) for one dose, 91·4% (26 443 of 28 922) for two doses, and 79·4% (15 440 of 19 436) for three doses in infants. The one-dose (77·1%, 16 422 of 21 305) and two-dose (69·0%, 14 704 of 21 305) coverage was highest in adolescents born in 2003 (approximately year 10 students). 2 years after implementation of the childhood vaccination programme, incidence of serogroup B meningococcal disease was significantly reduced compared with before programme implementation in infants aged 12 weeks to 11 months (adjusted IRR [aIRR] 0·40 [95% CI 0·23-0·69], p=0·0011), but not in those aged 1 year (0·79 [0·16-3·87], p=0·77), 2 years (0·75 [0·18-3·14], p=0·70), or 4 years (3·00 [0·47-18·79], p=0·24). aIRRs were not calculable in those aged 3 or 5 years because of no cases occurring after programme implementation. aIRR for serogroup B meningococcal disease was 0·27 (0·06-1·16, p=0·078) in adolescents aged 15-18 years 2 years after implementation of the adolescent and young adult programme, and 1·20 (0·70-2·06, p=0·51) in those aged 19-21 years in the first year. Two-dose vaccine effectiveness against serogroup B meningococcal disease was estimated to be 94·2% (95% CI 36·6-99·5) using the screening method and 94·7% (40·3-99·5) using the case-control method in children, and 100% in adolescents and young adults (no cases reported after implementation). Estimated two-dose vaccine effectiveness against gonorrhoea in adolescents and young adults was 32·7% (8·3-50·6) based on the case-control method using age-matched individuals with chlamydia infection as controls., Interpretation: 4CMenB vaccine shows sustained effectiveness against serogroup B meningococcal disease 2 years after introduction in infants and adolescents, and moderate effectiveness against gonorrhoea in adolescents. The high vaccine effectiveness against serogroup B meningococcal disease is likely due to high coverage in the target age groups and close antigenic match between the 4CMenB vaccine and the disease-associated serogroup B meningococcal strains circulating in South Australia. COVID-19-related physical distancing policies might have contributed to further declines in serogroup B meningococcal disease cases during the programme's second year., Funding: SA Health, Government of South Australia., Competing Interests: Declaration of interests HM is an investigator on vaccine trials sponsored by the GSK group of companies, Pfizer, Sanofi, and Merck. The institution of HM, MM, PA, and BW receives funding for investigator-led studies from industry, including Pfizer and Sanofi Pasteur. HM, MM, PA, and BW receive no personal payments from industry. All other authors report no competing interests., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Invasive meningococcal disease causes significant morbidity and mortality worldwide, with serogroup B being one of the predominant serogroups in Australia for many years. The South Australian (SA) State Government recently funded the introduction of a 4CMenB vaccination program for infants, children and adolescents. In addition to protecting against invasive meningococcal disease, emerging evidence suggests the 4CMenB vaccine may also be effective against gonorrhoea due to genetic similarities between Neisseria meningitidis and Neisseria gonorrhoeae . The proposed project aims to evaluate the effectiveness of the SA 4CMenB vaccination program against invasive meningococcal disease and gonorrhoea through a combination of observational studies using routine surveillance and research data. The main methodological approaches involve an interrupted time series regression model, screening, and case-control analyses with different sets of controls to estimate vaccine impact and effectiveness. These analyses are designed to minimize potential biases inherent in all observational studies and to provide critical data on the effectiveness of the 4CMenB vaccine against two diseases of major global public health concern.