Disclaimer: Early release articles are not considered as final versions. Any changes will be reflected in the online version in the month the article is officially released.
Volume 30, Number 10—October 2024
Dispatch
Mpox Epidemiology and Vaccine Effectiveness, England, 2023
Suggested citation for this article
Abstract
Reported mpox cases in England continued at a low but steady frequency during 2023. Of 137 cases reported in 2023, approximately half were acquired overseas and half were in vaccinated persons. Estimated effectiveness of 2-dose vaccine was 80%, and no vaccinated mpox patient was hospitalized.
In England, after the July 2022 peak in the mpox outbreak (1), which affected primarily gay, bisexual, and other men who have sex with men (GBMSM), cases declined and remained low into 2023 (2). We analyzed the epidemiology of postpeak mpox cases in 2023 in England, describing case-patient characteristics including vaccination status and providing an updated estimate of Modified Vaccinia Ankara–Bavarian Nordic (MVA-BN) vaccine effectiveness (VE).
We extracted records of confirmed and highly probable mpox diagnoses reported during January 1–December 31, 2023, from the UK Health Security Agency (UKHSA) Second Generation Surveillance System (SGSS) and deduplicated them by using specimen and patient identifiers. We defined a confirmed case as a positive monkeypox virus–specific PCR result and a highly probable case as a positive Orthopoxvirus PCR result (3). SGSS receives positive test results from all diagnostic laboratories in England (4). Because mpox is notifiable in England (5), reporting to SGSS is probably complete. UKHSA local Health Protection Teams collected self-reported epidemiologic and behavioral information (including vaccination status). NHS England provided aggregate data for mpox vaccinations administered in 2022 and 2023. We estimated overall VE by using the screening method (6). For the primary VE analysis, the eligible GBMSM denominator was 89,240 and was 20% higher at 107,088 according to a sensitivity analysis, similar to previous analyses (7). We estimated the proportion of GBMSM vaccinated by matching each case to the 1- and 2-dose coverage at the time, 2 weeks before persons became case-patients, then averaging the matched coverage across cases. For the 22 case-patients for whom vaccination status was unknown, we assumed that they would be distributed among those with 0, 1, and 2 doses in the same ratio as the observed ratio for these groups, to give a corrected value. We tested the difference between 1-dose and 2-dose VE estimates by using the Pearson χ2 test at 5% significance.
During January 1–December 31, 2023, a total of 137 mpox cases were reported (Appendix Figure), 135 confirmed and 2 highly probable. Most case-patients (105/137 [77%]) were London residents, comparable to case-patients in 2022 (Table 1). Of the 137 case-patients, 64 (47%) reported no travel outside the United Kingdom in the 21 days before symptom onset, indicating probable acquisition in the United Kingdom; 58 (91%) of the 64 identified as GBMSM. Of the 137 case-patients, 53 (39%) reported international travel, among which 43 (81%) identified as GBMSM and reported traveling to Europe, the Middle East, Asia Pacific region, and North America.
Most case-patients identified as GBMSM (107/137 [78%]); another 21 were adult men without recorded information about sexual orientation and no travel to the mpox-endemic countries in Central or West Africa. We included all of them as part of the 2022–2023 global clade IIb mpox outbreak, totaling 128 case-patients. Of the 9 case-patients excluded from the subsequent analysis, 8 were directly or indirectly linked to an mpox-endemic country; sporadic cases were distributed across time, and case-patients were heterosexual persons or children.
Most case-patients associated with the outbreak were HIV negative (69/128 [54%]), of whom most (51/69 [74%]) were taking HIV preexposure prophylaxis. Of the 128 HIV-negative case-patients, 28 (22%) reported attending an event involving sexual contact with multiple partners, and 24 (19%) had received a concurrent diagnosis of a sexually transmitted infection (Table 2).
Almost half of the case-patients with known vaccination status were fully or partially vaccinated (>1 dose) (52/106 [49%]), among whom 30 received >2 doses, 20 received 1 dose, and 2 did not report the number of doses. Among vaccinated case-patients, 20 (38%) reported attending an event involving sexual contact with multiple partners.
During July 2022–December 2023, a total of 77,543 GBMSM in England were vaccinated against mpox, 32,983 with 1 dose and 44,560 with 2 doses. MVA-BN vaccine coverage at the end of December 2023 was estimated at 37% for 1 dose and 50% for 2 doses (87% for 1 or 2 doses). Most vaccines had been given by March 2023 (91% first doses and 76% second doses).
VE of 1 dose was estimated at 84% (95% CI 74%–91%) (Table 3), comparable to the previous estimate of 78% (7). The VE of 2 doses was marginally, but not statistically significantly, lower than 1 dose, at 80% (95% CI 69%–83%) (p = 0.40). Overall VE of 1 or 2 doses was 82% (95% CI 74%–88%). Sensitivity analysis resulted in VE estimates that were markedly lower (Table 3), demonstrating that the method is affected by the estimated GBMSM population size.
Among known vaccinated case-patients in 2023, none were hospitalized. Of 11 (9%) persons who required hospital treatment for mpox, 9 were unvaccinated and vaccination status was unknown for 2.
The low numbers of mpox cases in 2023 were initially interpreted as the final few cases of the 2022 outbreak (1). However, throughout the year, cases continued steadily, split evenly between imported infections and community transmission. The demographic and behavioral characteristics of mpox case-patients in 2023 remained comparable to those in 2022 (Table 1), indicating that mpox continues to circulate predominately within GBMSM sexual networks.
Nearly half of outbreak case-patients in 2023 were vaccinated, and there were more cases among those who had received 2 doses of MVA-BN vaccine than among those who had received 1 dose. Our analysis, based on full-year data from 2023, demonstrates that VE of 1 or 2 doses remains high (82%). The estimated VE for 2 doses compared with 1 dose was marginally lower, but the difference was not statistically significant. Considering that first doses will have been given farther in the past than second doses and that 2 doses would be expected to confer more protection, that finding is counterintuitive and may reflect differences in risk behavior among those who came forward for a second dose because they may also be at greater risk for exposure to monkeypox virus. Our observation is consistent with reports from other high-income countries with outbreaks predominantly among GBMSM. In May 2023, the Chicago Department of Public Health (Chicago, IL, USA) noted that most of the cases reported since mid-April were among men who had received 2 doses of MVA-BN vaccine (9), yet a higher number of first doses had been given compared with second doses overall (10).
We found that no vaccinated persons had been hospitalized for mpox in 2023, indicating that the MVA-BN vaccine probably protects against severe disease requiring hospitalization. Our finding is corroborated by a global case series that found illness among vaccinated persons to be less severe (11).
Among the limitations of our analysis, we were unable to examine VE in different population groups, because of unavailability of corresponding disaggregated coverage data. In addition, hospitalization resulting from clinical need was used as a proxy for severity, a pragmatic decision based on the unavailability of data using an objective measure.
Overall, the experience in England during 2023 was of continued low-level community transmission among GBMSM, as well as imported infections, which will probably continue. Given that ≈20 countries continued to report mpox cases in December 2023 and the World Health Organization assessment that the overall global risk for GBMSM remains moderate (12), continued low-level transmission is likely before elimination is reached. Our findings highlight the value of continued active prevention through vaccination and health promotion to persons at higher risk and ongoing surveillance to examine factors that contribute to continued transmission.
Dr. Charles is a principal epidemiologist at the UKHSA and was involved in the UK response to the global 2022 mpox outbreak. Her particular interest is outbreak investigation and real-time surveillance of sexually transmitted infections.
Acknowledgments
We thank NHS England for their collection and sharing of vaccination data for the mpox vaccination program and sexual health services for delivering the vaccines. We also thank the UKHSA Health Protection Teams for collecting epidemiologic information during public health management of cases.
No external funding was received for this work.
H.C. led the epidemiologic analysis and drafted the manuscript. K.T. and K.F.B. validated the epidemiologic data analysis. N.A. led the VE analysis. All co-authors contributed to interpretation of the findings and to revision of the manuscript.
Our analysis was undertaken for health protection purposes under permissions granted to the UKHSA to collect and process confidential patient data under Regulation 3 of The Health Service (Control of Patient Information) Regulations 2020 and Section 251 of the National Health Service (NHS) Act 2006.
References
- UK Health Security Agency. Monkeypox outbreak: technical briefing 8 [cited 2024 Feb 14]. https://www.gov.uk/government/publications/monkeypox-outbreak-technical-briefings/investigation-into-monkeypox-outbreak-in-england-technical-briefing-8
- UK Health Security Agency. Mpox (monkeypox) outbreak: epidemiological overview [cited 2024 Feb 14]. https://www.gov.uk/government/publications/monkeypox-outbreak-epidemiological-overview
- UK Health Security Agency. Mpox (monkeypox): case definitions [cited 2024 Feb 14]. https://www.gov.uk/guidance/monkeypox-case-definitions
- UK Health Security Agency. Reporting to UKHSA: a guide for diagnostic laboratories [cited 2024 Feb 14]. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1159953/UKHSA_Laboratory_reporting_guidelines_May_2023.pdf
- UK Health Security Agency. Notifiable diseases and causative organisms: how to report [cited 2024 Feb 14]. https://www.gov.uk/guidance/notifiable-diseases-and-causative-organisms-how-to-report
- Flannery B, Andrews N, Feikin D, Patel MK. Commentary: Estimation of vaccine effectiveness using the screening method. Int J Epidemiol. 2023;52:19–21. DOIPubMedGoogle Scholar
- Bertran M, Andrews N, Davison C, Dugbazah B, Boateng J, Lunt R, et al. Effectiveness of one dose of MVA-BN smallpox vaccine against mpox in England using the case-coverage method: an observational study. Lancet Infect Dis. 2023;23:828–35. DOIPubMedGoogle Scholar
- UK Health Security Agency. HIV action plan monitoring and evaluation framework [cited 2024 Apr 25].[REMOVED HYPERLINKB0036ECA5C0100 FIELD] https://www.gov.uk/government/publications/hiv-monitoring-and-evaluation-framework
- Chicago Health Alert Network. Potential risk for new mpox cases—provider update: May 9, 2023 [cited 2024 Feb 14]. https://emergency.cdc.gov/han/2023/han00490.asp
- Chicago Department of Public Health. Mpox dashboard [cited 2024 Feb 14]. https://www.chicago.gov/city/en/depts/cdph/provdrs/infectious_disease/supp_info/mpox-home/mpox-dashboard.html
- World Health Organization. Multi-country outbreak of mpox: external situation report #31—22 December 2023 [cited 2024 Feb 14]. https://www.who.int/publications/m/item/multi-country-outbreak-of-mpox--external-situation-report-31---22-december-2023
Figure
Tables
Suggested citation for this article: Charles H, Thorley K, Turner C, Bennet KF, Andrews N, Bertran M, et al. Mpox epidemiology and vaccine effectiveness, England, 2023. Emerg Infect Dis. 2024 Oct [date cited]. https://doi.org/10.3201/eid3010.240292
Original Publication Date: August 27, 2024
Table of Contents – Volume 30, Number 10—October 2024
EID Search Options |
---|
|
|
|
Please use the form below to submit correspondence to the authors or contact them at the following address:
Hannah Charles, UK Health Security Agency, 61 Colindale Ave, London, NW9 5EQ, UK
Top