Kenyon (2019) is correct to suggest that there is limited evidence of longer term effectiveness. However caution is also warranted on making a firm conclusion that the vaccine has no longer term effectiveness because the evidence for this is also limited. There was a lack of power in both studies, due to at least two factors, to examine a longer term effect. This is different from an effect not being there. These factors were (1) a much smaller proportion of younger, unvaccinated individuals, and (2) many of younger vaccinated individuals within the cohort would not have been at risk yet because at the time of the study they were unlikely to be sexually active. The effect of a booster has also not been considered. It may be worthwhile revisiting the data in a few years to look again at this younger cohort.
Finally, risk of gonorrhoea for most people declines dramatically once they reach 30 years of age, so a lifetime of vaccine effectiveness is less important for population management of gonorrhoea compared to other infectious disease such as influenza or pneumonia.
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