The head of the World Health Organisation has been forced to pull out of an event in Britain after the US announced its intention to withdraw from the global health body.

Dr Tedros Adhanom Ghebreyesus, director general of the WHO, was supposed to speak online to an event of the think tank Chatham House.

But he was forced to pull out at the last minute after the United States formally notified the United Nations of its intention to terminate US participation in the WHO.

US president Donald Trump has been highly critical of the global health body in its response to the coronavirus pandemic.

Chatham House has been providing a weekly briefing on Covid-19 with eminent epidemiologist Professor David Heymann.

The infectious disease specialist, widely credited with shutting down the 2003 Sars outbreak, said without US funding, the WHO will “struggle” to keep it polio surveillance activities going.

Prof Heyman, distinguished fellow in Chatham House’s global health programme, said: “As an American, I’m very disappointed that the US would even be considering withdrawing from an organisation, which has benefited the US and countries around the world.

“I have to claim bias because I’m an American citizen and I’ve worked on secondment at the World Health Organisation.

“But the US has been behind incredibly important activities of WHO – during the Cold War, it was Russia and the United States who got together – despite these geopolitical tensions – and passed a resolution through the World Health Assembly that eradicated smallpox.

“So even despite geopolitical tensions in the 50s and 60s, the world moved ahead and eradicated the disease working through WHO.

“The world is working through WHO on polio eradication – another resolution that was passed by the US being stimulated to do that by Rotary International, which mobilised over a billion US dollars to contribute to polio eradication.

“WHO also can work in countries that the US can’t work in because of various regulations within the US. By giving its funding to WHO – which it has done freely in the past – WHO has been able to work in these countries that are problem countries for US politics, which are important in the global fight against infectious diseases.

“So the US has been a remarkable member of WHO, as has been the UK, and many other countries which have contributed both to the core budget, through their assessed contributions, and also as well through extra budgetary resources provided to specific activities.

“Without the US’s input into polio eradication, for example, WHO will struggle to keep its surveillance activities going, which are necessary to identify where polio is occurring, where it needs to be stamped out.

“So, the US contributions have been in really unimaginable to the general public, but have been, basically, along with the UK, Japan, and certain other G7 countries … the backbone of what the World Health Organisation has done.”

The US is the agency’s largest donor and provides it with more than 400 million US dollars per year.

Prof Heymann added: “I’ve always said in my own personal life, that things will go on if I go out and get run over by a bus tomorrow and I think that’s the attitude that we have to have with WHO.

“If the US does decide through its parliament, or congressional procedures to withdraw from WHO entirely, then WHO will get on with its work without an important partner, but it can be that partner can be replaced by others.

“Germany has become a very important partner in global health recently and other countries are stepping up as well.

“So, as much as it would be terrible if the US leaves WHO and leaves that expertise that is provided throughout the years, the WHO would continue to function, and other countries would likely step in to help support.”