Photo credit: www.sciencedaily.com
A recent study conducted by Charité — Universitätsmedizin Berlin has revealed that a single dose of the Imvanex vaccine offers an 84% effectiveness in preventing Mpox. However, this level of protection is insufficient for individuals living with HIV, emphasizing the need for all at-risk populations, particularly those with HIV, to receive the recommended second dose of the vaccine. These findings have been published in the journal The Lancet Infectious Diseases.
The emergence of the Mpox virus as a global health threat in 2022 prompted Germany’s Standing Commission on Vaccination (STIKO) to recommend Imvanex vaccinations for individuals at higher risk of infection. Initially developed to combat smallpox, the Imvanex vaccine received approval from the European Medicines Agency (EMA) to be utilized against Mpox in July 2022, marking a significant response to the public health crisis. Mpox shares a lineage with the original smallpox virus (Variola major), leading to the EMA’s decision based on laboratory evidence indicating the vaccine’s cross-protective properties. Nonetheless, the specifics of these protective benefits, especially for vulnerable groups, had remained unclear until now.
To gain deeper insights into the vaccine’s effectiveness, the EMA commissioned a comprehensive study led by Prof. Leif Erik Sander, Director of the Department of Infectious Diseases and Critical Care Medicine at Charité, alongside his research team at the Berlin Institute of Health at Charité (BIH). This study is notable for being the first to evaluate the vaccine’s effectiveness in populations stratified by HIV status. “Our findings confirm that a single dose of the vaccine provides substantial protection against Mpox, at least temporarily,” stated Sander. “However, this protection pertains only to individuals who are not living with HIV. We discovered that even those with HIV on effective treatment do not achieve adequate immunity from a single dose.”
The study, conducted from July 2022 to December 2023, involved over 9,300 participants, primarily men and trans individuals who reported sexual contact with men or other trans individuals. Half of the subjects received a single dose of the Imvanex vaccine, while the other half did not receive vaccination at all. Participants were followed for an average period of two months to track instances of Mpox infection.
The results indicated that significantly fewer cases of Mpox were observed among vaccinated individuals without HIV compared to their unvaccinated counterparts, reflecting the 84% effectiveness rate of the vaccine. “This is an impressive statistic, likely enhanced by receiving a second dose,” noted Sander. However, due to a notable decline in infections during the latter part of 2022, the study could not fully assess the benefits of the additional vaccine dose.
In stark contrast, only a minimal, statistically insignificant protective effect was detected for participants living with HIV. “The underlying issue is that developing effective immune protection post-vaccination depends on the presence of specific immune cells called T cells,” explained the infectious disease expert. “Individuals with HIV often present lower levels of these T cells, which are crucial for a robust immune response. This aligns with our observation where those with HIV reported fewer local and systemic side effects following vaccination.”
Prof. Florian Kurth, Head of the Clinical Infection Research Group at Charité and a key investigator in this study, underscored the importance of completing the two-dose regimen for all, particularly for those living with HIV. “We believe people with HIV would likely build sufficient immunity against Mpox after their second dose and strongly recommend adhering to the vaccination schedule provided by STIKO,” Kurth said. “Similarly, all other at-risk individuals should also complete the full two-dose course. Typically, the immune system strengthens its defense with multiple exposures to the vaccine.” Further research will be necessary to elucidate the specific protective effects across various demographics following complete vaccination.
In addition, the research team found that participants who were vaccinated yet still contracted the virus tended to experience milder symptoms. Those vaccinated exhibited fewer pox lesions that also healed more rapidly, and reported a reduced incidence of systemic manifestations such as fever. “We hypothesize that a second vaccination may further diminish symptom severity,” Kurth added. “Fewer pox lesions could also play a role in lessening the risk of virus transmission, making full vaccination critical in preventing Mpox outbreaks.”
The study also assessed the vaccine’s tolerability and safety among more than 6,500 individuals. The primary side effect reported was local pain at the injection site, with less than 3% of participants experiencing more severe symptoms like fever, headaches, muscle pain, nausea, or diarrhea. “Overall, the Mpox vaccine appears to be safe and well-tolerated,” Kurth summarized. “It is crucial to remember that full immune protection develops approximately 14 days post-vaccination. Additionally, individuals should continue to practice general preventive measures, such as using condoms, to mitigate the risk of sexually transmitted infections.”
The data regarding vaccine effectiveness pertains specifically to clade IIb of the Mpox virus, which was prevalent in Germany during the study. However, since clade IIb is closely related to clade I, which is currently spreading in Central Africa and adjacent regions, the researchers anticipate a high level of cross-protection. Thus, the implications of this study may extend to the ongoing clade I outbreak observed in Africa. The duration of immunity conferred by the vaccine remains uncertain, and the research team plans to pursue long-term studies while also looking into the potential benefits of a third vaccine dose.
About Mpox: Mpox, formerly known as monkeypox, is caused by a virus related to smallpox. Its symptoms parallel those associated with smallpox, which was eradicated in 1980. Unlike smallpox, Mpox typically has a milder course of illness. Individuals often experience symptoms such as fever, headaches, muscle and back pains, and swollen lymph nodes, followed by the appearance of pustules that can be extremely itchy and painful. Although fatalities linked to Mpox are rare, primarily occurring in children and immunocompromised individuals, severe cases can lead to significant scarring and other long-term complications. The Mpox virus spreads through close physical contact.
About Mpox infection rates: Diverse genetic variations categorize the Mpox virus into different clades. Following a global outbreak of clade IIb starting in May 2022, the virus predominantly spread through close physical and sexual contact, resulting in over 100,000 recorded cases across 122 countries. Infection rates across Europe have significantly decreased since the end of 2022; however, several countries, including the USA, Brazil, and Argentina, reported over 1,000 new cases in 2024. Recently, clade IIb cases have emerged in Australia, South Africa, and South America, while an increase in clade I Mpox infections, including a new variant Ib, has been noted in Africa, particularly in the Democratic Republic of the Congo. The World Health Organization (WHO) classified the clade II outbreak as a public health emergency of international concern (PHEIC) in 2022, followed by a similar declaration for the clade I outbreak in 2024.
About the Mpox vaccine: Germany’s Standing Commission on Vaccination (STIKO) endorses vaccination against Mpox using Imvanex, a vaccine authorized in the EU. Initially approved for smallpox in 2013, it obtained authorization for Mpox in July 2022. The vaccine is also recognized in the USA and Canada, where it is known as Jynneos and Imvamune. Imvanex is a live-attenuated vaccine containing non-replicating viruses, based on a weakened cowpox virus (modified Vaccinia virus Ankara, MVA vaccine), enabling it to induce cross-immunity against other pox viruses. STIKO recommends the vaccine for specific groups, including men over 18 who frequently change sexual partners, and lab personnel working with infectious Mpox samples. The basic immunization protocol consists of two doses.
About the study: The study was divided into two groups to investigate the vaccine’s tolerability and effectiveness. In the arm focused on safety and tolerability, researchers prospectively followed approximately 6,500 individuals. In the effectiveness arm, a rolling cohort design mimicking a target trial was applied, retrospectively comparing data between over 9,300 vaccinated and unvaccinated individuals with similar demographic and clinical profiles. Across all participants, the overall average effectiveness of the vaccine was found to be 58%. This research was funded by BIH and the EMA.
Source
www.sciencedaily.com