The European Union’s drug regulator said  it had started formally reviewing the use of a smallpox vaccine to treat a growing number of cases of monkeypox.

Imvanex was authorised by the European Medicines Agency (EMA) in 2013 for smallpox, but its maker, Danish firm Bavarian Nordic, did not apply at the time for its use against monkeypox.

Monkeypox is related to smallpox, which killed millions around the world every year before it was eradicated in 1980, but has far less severe symptoms.

The EMA said it had “started a review of data to extend the use of the smallpox vaccine Imvanex to include protecting people from monkeypox disease”.

It did not say when it could reach a decision, adding that it was waiting for a formal application from Bavarian Nordic.

The EMA also said that due to a shortage of supplies European countries should be able to import the American version of Imvanex, which is called Jynneos.

US authorities have already cleared Jynneos for use against monkeypox.

“Supplies of Imvanex are currently very limited in the EU,” the EMA said.

The World Health Organization said Saturday that a monkeypox outbreak that began in May was a deeply concerning evolving threat but did not currently constitute a global health emergency.

A surge of monkeypox cases has been detected since early May outside of the West and Central African countries where the disease has long been endemic. Most of the new cases have been in Western Europe.