Health authorities are running out of time in the battle to control the global monkeypox outbreak, according to medical experts who say funding, awareness and equitable access to vaccines are essential to prevent the spread of the virus.

In just over two months the outbreak has led to 15,000 cases in non-endemic countries, predominantly in Europe, prompting the World Health Organizational, or WHO, to declare a Public Health Emergency of International Concern, or PHEIC, on Saturday, which is the health body’s highest level of alert.

Hugh Adler, a clinical research fellow at the Liverpool School of Tropical Medicine, said that initially, he had predicted monkeypox would be easily controlled.

“The ongoing spread of monkeypox … has taken the global public health community by surprise,” Adler said.

The “window of opportunity is closing fast” to control the outbreak, he added, calling on governments to prioritize research funding and vaccination campaigns. The smallpox vaccine is thought to be 85 percent effective against monkeypox because of similarities between the viruses, though clinical trial data in this area is limited.

“The rate of spread of monkeypox has not slowed, and public health strategies have not shown a high rate of success,” Adler said. “We have more data showing that monkeypox is presenting in atypical ways, that contact tracing is a massive challenge given the unique circumstances of this outbreak, and that countries are struggling to access vaccine supplies.”

The United Kingdom health department said that vaccines are in limited supply. It is only offering jabs to high-risk groups, including some health workers, people who have come in close contact with individuals with infections, and men who have sex with multiple male partners. The majority of UK transmissions have occurred in the latter group.

Danish company Bavarian Nordic makes the most commonly used smallpox vaccine, which is referred to either by its generic name MVABN or brand names Imvanex, Imvamune and Jynneos. The company has an annual capacity of around 40 million jabs, and several countries have placed fresh orders this year. The United States has received 13 million doses in 2022, according to health analytics company Airfinity, adding to a large stockpile of 28 million MVA-BN jabs and tens of millions of older smallpox vaccines.

Other recent orders have been far smaller. Canada has requested 40,000 jabs and the UK has ordered 24,500, with both nations committing to a so-called ring vaccination strategy, where close contacts of people with infections receive treatment.

Several nations around the globe have stockpiles of smallpox vaccines, in part due to fears that the virus could be used as a biological weapon. The WHO has called for a global audit of smallpox jabs and for countries to engage in talks over the fair distribution of treatments to nations struggling to contain monkeypox. The US has enough smallpox vaccine stockpiled for its entire population, according to the Centers for Disease Control and Prevention.

Boghuma Titanji, an assistant professor of medicine at Emory University in the US, is hopeful that the recent WHO public health alert will encourage international collaboration.

“It is also an opportunity to get things right on global health equity and access to resources such as testing, vaccination, and antiviral medications, which are areas in which historically we have seen many failures, resulting in countries with limited resources being left behind,” Titanji said.