The efficacy of the monkeypox vaccine works at more than 78%, and this, as early as two weeks after the first dose, according to data from the British Health Safety Agency published Monday, November 21.

The scientific report looked at 363 cases of monkeypox recorded in England between July 4 and November 3 among the population eligible for the vaccine. Of these cases, only eight had been vaccinated at least two weeks before becoming ill and 32 had received a dose within 13 days of contracting the virus.

“This gives an estimated vaccine efficacy for a single dose of 78% after 14 days,” the health agency UKHSA said in a statement Tuesday, Nov. 22.

“We now know that a first dose of vaccine provides strong protection against monkeypox,” said Jamie Lopez-Bernal, epidemiologist for UKHSA. And “even if cases of monkeypox are few, it is vital to remain vigilant about the risks,” he warned.

On the other hand, the head of vaccinations at the NHS, Steve Russell, said that “more than 55,000 doses of vaccine have already been administered” in England. The Bavarian Nordic vaccine, marketed under the name Jynneos in the United States, is the only one approved specifically against monkeypox. It is administered in two doses, 28 days apart.

By the end of the summer, U.S. data showed that the vaccine was highly effective after the first dose, with unvaccinated people 14 times more likely to be infected with monkeypox than those vaccinated.

The disease -endemic in some West African countries- is characterized by rashes, which can appear on the genitals or in the mouth, and can be accompanied by fever, sore throat or pain in the lymph nodes.

Beginning in May, health authorities noted outbreaks in Europe and the United States, but the epidemic is now in full retreat.