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

In just more than two months, the outbreak has led to 15,000 cases, predominantly in Europe, prompting the World Health Organization to declare a Public Health Emergency of International Concern 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 he had initially 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.

Vaccine shortages

"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," Adler said.

Public health experts in the United States have warned that the country is running out of time to contain the monkeypox outbreak as nearly 3,000 confirmed cases have been reported in US.

The state of New York had the most cases, with 900, followed by California with 356 and Florida with 247, according to the latest data from the US Centers for Disease Control and Prevention.

Given the testing bottlenecks in the US, monkeypox cases are likely being undercounted, health experts said. The CDC confirmed two cases of monkeypox in children on Friday. One case is a toddler who is a resident of California. The other is an infant who is not a US resident.

"We're losing daylight," said Anne Rimoin, a professor of epidemiology at the Fielding School of Public Health of the University of California, Los Angeles.

"Every day that we aren't continuing to push forward on all fronts, the less likely it is that we will be able to contain it," she said.

The United Kingdom's health department said vaccines are in limited supply.

Danish company Bavarian Nordic makes the most commonly used smallpox vaccine, which is referred to either by its generic name MVA-BN 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 US has received 13 million doses this year, 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.