New Study Highlights Importance of Mpox Vaccination

People who were previously infected with mpox or were vaccinated against it had less severe disease and shorter disease duration, according to new research data published in The Lancet Infectious Diseases.¹

A global outbreak of mpox, which was formerly known as monkeypox, has been impacting men who have sex with men since 2022. Unlike smallpox, another orthopoxvirus in which previous infection or vaccination provides lifelong immunity, the recent mpox outbreak has been seen in people who had recently been infected or vaccinated.

Investigators from Queen Mary University of London conducted a case series study in an effort to “describe the epidemiological and clinical characteristics of mpox in individuals with past infection or vaccination to improve the understanding of this disease in the setting of previous immunity.”

The team of researchers gathered data from 9 countries that participated in the Sexual Health and HIV All East Research (SHARE) Collaborative. Investigators from locations across the globe that had a high burden of mpox were also invited to contribute. The study cohort included 38 patients, of which 8 had been infected with mpox after an initial infection and 30 were infected after vaccination with the Modified Vaccinia Ankara-Bavarian Nordic vaccine from May 11, 2022, to June 30, 2023.

The Mpox Severity Score System was used to assess the severity of symptoms, including number of active lesions, anatomical extent of lesion involvement, presence of confluent lesions, presence of bacterial superinfection, extent of mucosal areas affected, level of care, and analgesia requirement.

Investigators found that patients with natural immunity had a shorter disease course with less mucosal disease compared to their original infection. Patients who were vaccinated showed symptoms of few lesions, little mucosal disease, and minimal analgesia requirements. Of the vaccinated patients, 2 received oral tecovirimat.

Additionally, there were no deaths, no bacterial superinfections, and the majority of patients were managed in the ambulatory clinic. There was 1 hospital admission for a necrotizing neck lesion.

“This is good news and shows that post-vaccination infections are less severe and the need for hospitalization is lower,” Chloe Orkin, lead author on the study, said in a release.² “This is clear evidence that vaccination is an important tool in reducing morbidity and controlling further outbreaks.”

Study limitations include potential selection bias, the inability to compare data to the current outbreak, and the fact that hMPXV cycle threshold testing, viral load, genome sequencing, and immune response testing were not uniform.

“We have to ensure global access to vaccinations and treatments if we want to curb this global outbreak, especially in the African regions that have been historically worst affected and are still without access to vaccines or treatment for mpox,” said Orkin.

Reference

1. Hazra A, Zucker J, Bell E, et al. Mpox in people with past infection or complete vaccination course: A global case series. Lancet Infect Dis. Published online 2023. doi:10.2139/ssrn.4491622

2. New study shows effectiveness of mpox vaccine. News Release. Queen Mary University of London. September 5, 2023. Accessed September 8, 2023. https://www.qmul.ac.uk/media/news/2023/smd/new-study-shows-effectiveness-of-mpox-vaccine.html