Despite a steady decline in cases, the Mpox virus continues to circulate within key populations, underscoring the need for ongoing vaccination efforts and public health awareness.
Dispatch: Mpox Epidemiology and Vaccine Effectiveness, England, 2023. Image Credit: Kateryna Kon / Shutterstock
In a recent study published in the journal Emerging Infectious Diseases, researchers evaluated the epidemiology of mpox and the effectiveness of the Modified Vaccinia Ankara-Bavarian Nordic (MVA-BN) vaccine in England in 2023.
Mpox cases declined in England after peaking in July 2022, which mainly affected gay men, bisexual men, and other men who have sex with men (GBMSM) and remained low into 2023. However, cases continued at a steady frequency throughout 2023, signaling ongoing transmission. The World Health Organization (WHO) has assessed that the risk of mpox is moderate for GBMSM.
About the study
In the present study, researchers analyzed mpox epidemiology in England in 2023 and the effectiveness of the MVA-BN vaccine. They accessed the Second-Generation Surveillance System of the United Kingdom (UK) Health Security Agency for records of highly probable and confirmed mpox cases between January and December 2023. Records were deduplicated using patient and specimen identifiers.
A highly probable case had a positive Orthopoxvirus polymerase chain reaction (PCR) result. A confirmed case had a positive mpox virus-specific PCR result. Local health teams obtained self-reported behavioral and epidemiologic information. Mpox vaccination data were derived from the National Health Service (NHS) England. The overall vaccine effectiveness (VE) was calculated.
The proportion of vaccinated GBMSM was estimated by matching each case to the single- and double-dose coverage at the time, two weeks before individuals were case patients. Subsequently, the matched coverage was averaged. For some case patients with unknown vaccination status, the team assumed these cases to be distributed among those with zero, one, or two doses. Pearson chi-squared test examined differences between one- and two-dose VE estimates.
Findings
In 2023, 137 mpox cases were diagnosed. Only two cases were highly probable. Most mpox cases (77%) were residents of London, consistent with 2022 estimates. Sixty-four cases had not traveled outside the UK within three weeks before the onset of symptoms; of these, 58 individuals were GBMSM. Further, 53 cases reported international travel, including 43 GBMSM, with travel to the Middle East, Europe, North America, and the Asia Pacific.
Overall, 78% of cases were GBMSM. Twenty-one cases were adult males lacking information on sexual orientation and had no travel to mpox-endemic countries. Most cases (54%) were negative for human immunodeficiency virus (HIV). Of these, 74% were on HIV pre-exposure prophylaxis. Notably, 22% of HIV-negative cases reported attending an event involving sexual contact with multiple partners, and 19% had a concurrent sexually transmitted infection. Almost half of the cases were partially or fully vaccinated.
Among the vaccinated, 20 attended an event involving multiple sex partners. Between July 2022 and December 2023, 77,543 GBMSM were vaccinated for mpox. MVA-BN coverage by December 2023 was estimated at 50% for two doses and 37% for one dose, leading to an overall coverage of 87% among GBMSM. VE was 84% for a single dose and 80% for a double dose. Overall, VE was 82% for single or double doses. Sensitivity analysis suggested that VE estimates could be influenced by the size of the GBMSM population, indicating the potential variability in effectiveness. In 2023, none of the vaccinated persons were hospitalized. Of those hospitalized, nine were non-vaccinated, and two had an unknown vaccination status.
Conclusions
The low incidence of mpox cases in 2023 was initially presumed to be the final few cases from 2022. Nonetheless, cases increased steadily in 2023 and were evenly split between community transmission and imported infections. The demographic and behavioral characteristics of mpox cases in 2023 remained comparable to those in 2022, particularly within GBMSM networks. Thus, mpox continues to predominately spread within GBMSM networks. Almost half of cases in 2023 had been vaccinated.
One or two doses of MVA-BN had a VE of 82%. While VE was marginally lower for two doses than for one, the difference was not statistically significant. Of note, no vaccinated person was hospitalized for mpox in 2023. Taken together, England experienced a low-level community transmission of mpox among GBMSM. The authors speculate that low-level transmission will prevail before elimination is achieved.
To curb the spread of mpox, continued vigilance, including vaccination and health promotion among high-risk groups, remains essential.
Single dose of MVA-BN vaccine shows 58% effectiveness against mpox