The head of the World Health Organization says the US backing of a proposed waiver of intellectual property rights for COVID vaccines is a "monumental moment" in the fight against the virus.
A waiver - which Europe's leaders say they are now also ready to discuss - could significantly boost vaccine production around the world by lifting patents, copyrights and protections for industrial design and confidential information.
This could mean easier access to vaccines for those in poorer and middle-income countries, many of whom have been at the back of the queue while others such as the US and UK have been able to vaccinate large numbers of their own people.
But there were warnings from the pharmaceutical industry about potential harm to future innovation as well as the safety of vaccines being produced in a potential free-for-all.
Sceptics also pointed to other issues such as the apparent unwillingness of some countries to export vaccines, and production supply, rather than patents, being to blame for shortages.
The issue of global access to vaccines has become more urgent with the surge of cases in India, the world's second-most populous country.
WHO's director-general, Tedros Adhanom Ghebreyesus, has repeatedly urged the world to support the waiver proposal, which was initially brought to the World Trade Organisation (WTO) by India and South Africa in October last year.
After the announcement by the Biden administration, he said on Twitter: "This is a monumental moment in the fight against COVID-19.
"The commitment by (Joe Biden and US trade representative Katherine Tai) to support the waiver of IP protections on vaccines is a powerful example of United States leadership to address global health challenges."
More than 100 countries support the proposal and Mr Biden had been under growing pressure from a group within Congress - all fellow Democrats who backed the waiver.
European Commission president Ursula van der Leyen said the EU was "ready to discuss any proposals that address the crisis in an effective and pragmatic manner".
"That's why we are ready to discuss how the US proposal for a waiver on intellectual property protections for COVID-19 vaccines could help achieve that objective," she said.
France's President Emmanuel Macron said he was "very much in favour" of opening up intellectual property.
However, a French government official said it was lack of production capacity and components that was the problem rather than patents, adding: "It is the United States which has not exported a single dose to other countries and which is now talking about lifting the patents."
The UK government said in a statement that it was "working with WTO members to resolve this issue" and was in discussions with countries including the US to try to boost COVID vaccine production and supply.
Britain has previously encouraged knowledge sharing between industry and manufacturers, but stopped short of calling for IP waivers.
Those in favour of the move say it is already among the WTO's tools and there is no better time to use it than during a pandemic that has killed 3.2 million people, infected more than 400 million more, and ruined economies around the world.
Earlier Ms Tai said: "This is a global health crisis, and the extraordinary circumstances of the COVID-19 pandemic call for extraordinary measures.
"The administration's aim is to get as many safe and effective vaccines to as many people as fast as possible."
But those against it say producing the vaccines is difficult and the process of vaccinating the world cannot be sped up simply by easing intellectual property laws.
Frankfurt-listed shares of Pfizer, Moderna and Novavax fell 5.2%, 8.2% and 10.1% respectively on Thursday, extending losses of up to 6% seen the previous day.
London-listed shares of AstraZeneca, which has sold its vaccine not-for-profit, did not move.
Adam John Ritchie, senior project manager and vaccine scientist at the Jenner Institute, was one of the key people involved in setting up manufacture for the AstraZeneca vaccine.
He said: "It feels like trying to fight the HIV drug battle all over again.
"The manufacturing of these vaccines is much more complex, thus tech transfer becomes more important.
"Supply chains are the real bottleneck right now anyway."
Dr Richard Torbett, who heads the Association of the British Pharmaceutical Industry, told Sky's Ian King Live there were real concerns over safety in the event of a production free-for-all.
Both also said that lifting such intellectual property protections could hurt future innovation - companies can spend a lot of money researching such breakthroughs and they rely on the protections to make sure their work is not then copied by others for easy profit.
Ms Tai has also warned it will take time to reach the global consensus needed to waive the protections under WTO rules and officials have said any effect on vaccine supply will not be immediate.
Also on Wednesday, WTO director-general Ngozi Okonjo-Iweala spoke to a gathering of ambassadors from developing and developed countries about the issue.
WTO spokesman Keith Rockwell said the countries agree on the need for wider access to COVID-19 vaccines and a panel has been set up to discuss the proposal at a "tentative" meeting later this month before a formal gathering in early June.
A consensus could take some time but Mr Rockwell said there had been a recent change in tone after months of arguing, adding that the discussion was now "far more constructive, pragmatic".
"It was less emotive and less finger pointing than it had been in the past," he said.
"I think that this feeling of everyone-being-in-it-together was being expressed in a way that I had not heard to this point."