A recent study from Charité - Universitätsmedizin Berlin has revealed that a single dose of the Imvanex vaccine provides an impressive 84% protection against the monkeypox virus. This finding is critical, particularly as the World Health Organization and health authorities worldwide continue to combat the recent outbreak of this viral infection.
However, the study indicates that one dose is insufficient for individuals living with HIV, necessitating a second dose for full protection. The findings were published in The Lancet Infectious Diseases, offering new guidance for vaccination strategies aimed at vulnerable populations.
The backdrop to this research lies in the serious MPox outbreak that began sweeping across the globe in 2022, which prompted the Standing Committee on Vaccination in Germany (STIKO) to recommend the Imvanex vaccine for at-risk populations. Originally developed to prevent smallpox, the Imvanex vaccine received European Medicines Agency (EMA) approval in July 2022, following considerable evidence supporting its efficacy against similar viruses.
Professor Leif Erik Sander, who heads the Department of Infectious Diseases and Tropical Medicine at Charité and led the study, emphasized that while the vaccine provides solid protection for most individuals, those with HIV present a different scenario. “Our results confirm that one vaccine dose offers good short-term protection against the monkeypox virus, particularly for individuals not infected with HIV,” Sander stated. “Unfortunately, our findings show that those living with HIV do not have sufficient protection after just one dose.”
The study compared the immune response of more than 9,300 participants, consisting of men at risk for MPox, and tracked their health outcomes from July 2022 to December 2023. Half of the participants received a single dose of Imvanex, while the other half remained unvaccinated. Over the course of two months, the study recorded substantially lower instances of monkeypox infections among the vaccinated group.
The study’s data revealed that the effectiveness of the vaccine stands at a robust 84% for HIV-negative individuals. For those infected with HIV, however, the protective effects appeared negligible. The immune response needed—a specific type of immune cell known as T-cells—was found to be often diminished in those with HIV. “This means the immune response is weaker, leading to a less effective reaction to the vaccine,” Sander noted.
The significance of these results is backed by empirical observations during the study. Participants who had been vaccinated and still contracted MPox experienced milder symptoms, fewer skin lesions, and faster recovery times. Additionally, they reported fewer systemic illness signs, such as fever. “We hypothesize that a second vaccination dose could further reduce these symptoms and enhance overall immunity,” Professor Florian Kurth, a leading researcher in the group, added.
STIKO's recommendations now stress that individuals at heightened risk, especially those living with HIV, should receive two doses of the vaccine for optimal immunity. Previous research had indicated that the immune system typically develops a more robust protective response after repeated exposure to a vaccine.
Kurth explained, “We advise all other at-risk groups to complete the two-dose regimen, as it encourages longer-term immunity. Knowing how our immune systems work, it stands to reason that multiple doses lead to stronger and more sustained immune responses.”
The study also focused on the vaccine's tolerance and safety, surveying over 6,500 individuals who received the Imvanex dose. The most frequently reported side effect was injection site pain, while less than 3% experienced notable symptoms such as fever, headaches, and gastrointestinal issues. Overall, Imvanex was deemed safe and well-tolerated by the vast majority of participants.
“It’s important to recognize that full immunity typically develops approximately two weeks after vaccination,” Kurth cautioned, highlighting the need for ongoing preventive measures alongside vaccination for those at risk.
As the global health community grapples with the implications of these findings, the researchers call for broader vaccination efforts against MPox to help curtail further outbreaks and protect vulnerable populations. "Full vaccination can significantly help in preventing the spread of the virus," Sander concluded.
This study emphasizes the ongoing need to adapt public health measures to include specific recommendations for individuals affected by chronic infections like HIV. Ensuring that all individuals receive complete and effective vaccinations will be essential as health officials work towards achieving comprehensive community immunity.
With the resurgence of infectious diseases asserting a sweeping impact on public health in recent years, the work by the Charité team stands as a critical step towards informed strategies for vaccination against the monkeypox virus.
