Abstract
BACKGROUND: 4CMenB appears to be effective in reducing Neisseria gonorrhoeae (Ng) infections. Aims are to assess factors associated with breakthrough rectal Ng after 4CMenB and evaluate clinical and microbiological characteristics of breakthrough infections compared with before vaccination. METHODS: This was a retrospective study of gay, bisexual, and other men who have sex with men (GBMSM) vaccinated with 4CMenB (2 doses) between 2017 and 2023 at the San Raffaele Scientific Institute for Research, Hospitalization and Healthcare (IRCCS San Raffaele Scientific Institute), Milan, Italy, and tested for rectal Ng. Rectal Ng infection is considered breakthrough if it occurs >1 month after the second 4CMenB dose and with positive nucleic acid amplification test (NAAT) result. Follow-up was from July 2017 (first 4CMenB vaccination) to November 2023 (data freeze). Rectal Ng was screened with both NAAT and gonococcal-specific cultures. Characteristics of individuals with or without breakthrough Ng and of Ng infections before or after 4CMenB were compared using Mann-Whitney and χ(2)/Fisher tests. RESULTS: Overall, 473 GBMSM vaccinated with 4CMenB were included, with a median age (interquartile range) of 43 (37-51) years; 451 of 473 were living with human immunodeficiency virus. The percentage of NAAT-positive rectal Ng swab samples was 76 of 957 (7.7%) after 4CMenB and 51 of 456 (11.1%) before. Breakthrough rectal Ng after baseline were 76 in 57 of 473 people. People with rectal Ng after 4CMenB were younger, more likely to have a previous sexually transmitted infection, and had more sexual partners than those without (all P < .001). Breakthrough rectal Ng infections were less frequently symptomatic (34.2% vs 66.7%; P = .001) and more likely with negative gonococcal-specific culture (55.3% vs 19.6%; P < .001) compared with before vaccination. CONCLUSIONS: Breakthrough rectal Ng infections after 4CMenB were 76 in 57/473 people, preferentially identified in GBMSM with higher-risk sexual behaviors, were less often symptomatic, and more often with negative gonococcal-specific cultures, suggesting lower infection virulence.