One of the teams racing to develop a coronavirus vaccine announced Monday that its drug had shown 90 percent effectiveness, sending markets soaring and raising hopes of an end to the pandemic.
US pharmaceutical giant Pfizer said tests involving more than 40,000 people had provided results that were a "critical milestone" in the search for a vaccine, as global infections soared past 50 million - including an alarming 10 million now in the US alone.
Stock markets had already jumped after Democrat Joe Biden was called as the winner of the US presidential election on the weekend. They accelerated rapidly on the vaccine news, with the Dow Jones Industrial Average up three percent at Monday's close of trade.
An effective vaccine is seen as the best hope to break the cycle of deadly virus surges followed by severe restrictions across much of the world since COVID-19 first emerged in late 2019.
Tens of millions of people in Europe are living under lockdowns preventing them from leaving their homes, and millions of business owners are enduring forced closures.
The drug, being developed jointly with German firm BioNTech, is one of more than 40 candidate vaccines, but no other has yet made similar claims about its effectiveness.
The scientific community reacted positively, with top US expert Anthony Fauci describing the results as "extraordinary."
WHO director Tedros Adhanom Ghebreyesus hailed the news as "encouraging" shortly after warning that the world "might be tired of COVID-19."
But others pointed out that no information had yet been disclosed about the ages of the participants in the trial.