Meningococcal disease and gonorrhea cause severe morbidity in Australian adolescents, particularly among Aboriginal People. The two diseases are caused by bacteria that are genetically related, but very different in their patterns of transmission and pathogenesis. Bacterial meningitis and sepsis from Neisseria meningitidis (often called meningococcus) can have severe outcomes including long-term disability, arising from neurological deficits and from necrotic skin and gangrene of the limbs requiring amputations. The case fatality rate is \~10%. A multicomponent meningococcal B (4CMenB) vaccine (Bexsero®) is approved and licensed for use against MenB disease in Australia but not funded on the National Immunisation Program (NIP) due to failure to meet cost effectiveness criteria. New emerging data suggest 4CMenB may also protect against gonococcal infection, a sexually transmissible infection (STI) which can infect the urethra, cervix, rectum, conjunctiva, and throat. If left untreated, gonorrhoea can lead to pelvic inflammatory disease, tubal scarring and ultimately infertility in females, and swelling and scarring in the epididymis or testicles in males. In the NT, notification rates for gonorrhoea in 15-19 year olds range from 1924/100,000 to 17,022/100,000 in Aboriginal young people and from 106/100,000 to 1081/100,000 in non-Aboriginal young people over different areas of The Territory (averaged over 2014-2018). At present there is no vaccine against gonorrhoea. Emerging evidence shows that the 4CMenB vaccine may have some protection against gonorrhoea due to genetic similarities that exist between the two organisms that cause meningitis and gonorrhoea. If the effectiveness of the 4CMenB vaccine against gonorrhoea can be demonstrated at a population level it would have substantial health benefits to be gained world-wide, but particularly for Aboriginal People.

Consenting 14-19 year olds will be asked to complete a 1-2 page questionnaire to collect information on risk factors for meningococcal disease and meningococcal carriage. A throat swab will be obtained and the first dose of the 4CMenB vaccine will be administered. Two-three months after the first dose, participants will receive the second dose of the 4CMenB vaccine. One year after the first dose, the participants will be asked to come for the third visit, where they will be asked to complete the same questionnaire that was completed during visit one and a throat swab taken. Throat swabs will be tested to detect the meningococcus bacteria which is carried in the throat of around 10% of people. Research in South Australia has shown double the rates of carriage in Aboriginal People compared to non-Aboriginal People.

The effectiveness of the 4CMenB vaccine against meningococcal carriage, invasive meningococcal disease and gonorrhoea will be evaluated using results of meningococcal carriage and routine surveillance data on IMD and gonorrhoea obtained from the Centre for Disease Control (CDC), the data custodian for notifiable diseases in the NT. The evaluations will include comparisons between vaccinated vs unvaccinated and number of notifications in post vs pre study implementation periods. The data on IMD and gonorrhoea notifications in the NT will be obtained from the Communicable Disease Control in the NT. The main methodological approaches involve an Interrupted Time Series regression model, screening approaches, and case-control analyses with different sets of controls to estimate vaccine impact and effectiveness