Efficacy of smallpox vaccines against Mpox infections in humans: Smallpox vaccine efficacy against Mpox

The Mpox virus (MPXV) is endemic in certain countries in Central and West Africa,
where several mammalian species, especially rodents, are natural reservoirs. However, the MPXV can infect non-human primates and cause zoonotic infections in humans after close-contact with an infected animal. Human-to-human transmission of MPXV can also occur through direct close contact with an infected individual or infected materials. In May 2022 an initial cluster of human Mpox cases was identified in the UK, with the first case confirmed in a patient that had recently travelled to Nigeria. The infection subsequently spread via human-to-human transmission within the UK and Mpox cases began to appear in many other countries around the world where the MPXV is not endemic. No specific treatments for MPXV infection in humans are available. However, data from studies undertaken in Zaire in the 1980’s revealed that those with a history of smallpox vaccination during the global smallpox eradication campaign also had good cross-protection against MPXV infection. However, the vaccines used during the global eradication campaign are no longer available. During
the 2022 global Mpox outbreak over a million doses of the Modified Vaccinia AnkaraBavarian Nordic (MVA-BN) smallpox vaccine were offered either as pre- or postexposure prophylaxis to those at high-risk of MPXV infection. Here, we review what has been learnt about the efficacy of smallpox vaccines in reducing the incidence of MPXV infections in high-risk close-contacts