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Modified smallpox vaccine effective against monkeypox

A research review has shed light on the efficacy and safety of the smallpox vaccine in combating the monkeypox virus.

Smallpox vaccines were found to be up to 80 per cent effective and very safe against monkeypox virus, now known as Mpox, after over 1 million doses were administered worldwide in a recent outbreak.

Researchers reviewed vaccination efforts involving a modified smallpox vaccine, using a significantly weakened version of the smallpox virus, as pre- or post-exposure protection against Mpox in high-risk close contacts.

Their results suggest that a single dose of the modified vaccine led to a significant reduction in the risk of Mpox infection of between 78 to 93 per cent.

This effectiveness closely paralleled the protection achieved by the original smallpox vaccines, which are no longer available to the public after smallpox was eradicated in 1980.

An advantage of this modified vaccine is the virus’ inability to replicate, in contrast to the original smallpox vaccines, ensuring that new viruses are not released in the body, experts say.

Global challenge

Researchers from the Roslin Institute reviewed studies on the use of smallpox vaccines during a 2022 outbreak in which the Mpox virus spread from Nigeria, one of several Central and West African countries where it is endemic, to cause infections in other countries, posing a global health challenge.

Their review, encompassing research in England, Spain, Israel, and the US, recognised some limitations in the studies, such as the predominant inclusion of men and younger participants.

Researchers also highlighted the significance of considering additional factors such as co-infection with parasites in future research, particularly in African regions where the Mpox virus is endemic.

This review was published in Immunotherapy Advances.

Throughout the 2022 outbreak, the modified smallpox vaccine emerged as a safe and effective tool to safeguard high-risk close contacts against symptomatic Mpox infection. Countries where the vaccine was administered witnessed a significant decline in Mpox cases.

“As the world moves forward, the lessons from this review underscore the importance of proactive measures to prevent future Mpox spillover events and limit the virus's chances of establishing itself in human populations.

Melissa Christodoulidou, undergraduate student who performed the analysis

The results of this analysis show that the use of the modern modified smallpox vaccine during the 2022 Mpox outbreak was a very safe and effective way to protect high risk close contacts from Mpox infection.

Professor Neil Mabbott

 ** The Roslin Institute receives strategic investment funding from the Biotechnology and Biological Sciences Research Council and it is part of the University of Edinburgh’s Royal (Dick) School of Veterinary Studies. **

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