Even as rich countries are hoarding smallpox vaccinations to counter the current monkeypox outbreak, protection from the virus may not last a lifetime, claimed a recent study published in the Lancet.

Globally, the monkeypox outbreak has seen more than 31,665 cases and 12 deaths, according to the World Health Organization, which recently declared the disease a public health emergency of international concern. At present, the majority of cases in current outbreaks are among men who have sex with men.

Although the smallpox jab has been shown to reduce the chance of symptomatic infection and severe illness from monkeypox, protection may decline over time. In the study, 32 of the 181 patients in Spain had previously received a childhood vaccination against smallpox.

Dr Oriol Mitja, a co-author of the research, said that since most participants who had been vaccinated against smallpox received the jab more than 45 years ago, it is reasonable to predict that their protection would have waned, the Guardian reported. "All I can say is that childhood vaccinations may not protect 100 per cent for life," he was quoted as saying.

According to Jimmy Whitworth, professor of international public health at the London School of Hygiene & Tropical Medicine, while the viruses are similar they are not identical, "so the cross-protection provided may not be absolute". Experts also claimed that HIV may be the reason why protection from the jab wanes over time, the report said.

The study showed that about 40 per cent of the monkeypox cases were in people who were HIV positive. Mitja said the figure was 60 per cent among those who had childhood smallpox vaccination but still got monkeypox. "(People with HIV) may have had some immunodeficiency, eroding away the protection from the vaccine," Whitworth was quoted as saying.

Research from scientists in the US, published in 2020, found immune responses to childhood smallpox vaccination declined faster among people who subsequently became infected with HIV. Prof. Mark Slifka, of Oregon Health & Science University, said: "This is a potential concern that may explain why there could be more monkeypox breakthrough cases in these current outbreaks."

But he urged caution in interpreting the data from Spain, noting that the childhood smallpox vaccine might still have provided partial immunity towards monkeypox, the report said.