British Department of Health officials said Tuesday the monkeypox vaccine was 78 percent effective and urged men who have sex with men to undergo vaccination.

The UK Health Safety Agency said its latest analysis “gives an estimate of vaccine efficacy for a single dose of 78 per cent 14 days or more after vaccination”.

It described the results as “the strongest British evidence yet” of the sting’s effectiveness.

Bavarian Nordic in Denmark is the only laboratory producing an approved monkeypox vaccine called MVA-BN.

It said last week it had signed a deal to provide European nations with up to two million doses of vaccine.

More than 55,000 doses of vaccine have been administered in England, said Steve Russell, NHS national director for vaccinations and screening.

“We now know how effective the vaccine is, providing 78 percent protection against the virus with just one dose.”

The recent monkeypox outbreak began spreading around the world in May and peaked in July.

The UKHSA said its findings were based on analyzing 363 cases of monkeypox between July and November in England.

Most cases have involved gay and bisexual men and others who have sex with men. Of those who contracted the virus, 323 were unvaccinated.

“We now know that a single dose of vaccine provides strong protection against monkeypox, showing the importance of vaccination to protect yourself and others,” said Jamie Lopez-Bernal, UKHSA’s consultant epidemiologist.

“A second dose is expected to provide even greater and longer-lasting protection,” he added.

There have been 3,570 confirmed cases of monkeypox in the UK, which causes fever, muscle pain and large, boiling skin lesions.