Two experts on an international mission to investigate the origins of Covid-19 in China are still in Singapore after testing positive for Covid antibodies, the WHO said Thursday.

The World Health Organization said earlier that the international team of experts had landed in Wuhan for the long-delayed mission, but it later tweeted that two had yet to make it there.

“Two scientists are still in #Singapore completing tests for #COVID19,” the UN health body said in a tweet.

“All team members had multiple negative PCR and antibody tests for Covid-19 in their home countries prior to travelling,” it said.

But it added that the team of more than a dozen experts had been tested again during a stopover in Singapore.

WHO said all members were negative for PCR, which determines whether a person is currently infected with Covid-19.

But two members had tested positive for so-called IgM antibodies, which are usually the first antibodies produced by the immune system when a virus attacks.

When IgM is detected, the subject could still be infected or may recently have recovered from a Covid-19 infection.

WHO said the two were currently being retested for IgM as well as IgG antibodies, which generally appear a week or so after Covid-19 symptoms begin and indicate that you recently were infected with the virus.

The WHO has for months been working to send the team of international experts, including epidemiologists and animal health specialists, to China to help probe the animal origin of the novel coronavirus pandemic and how the virus first crossed over to humans.

The WHO says establishing the pathway of the virus from animals to humans is essential to preventing future outbreaks.

The virus was first detected in Wuhan in late 2019 and has since spread across the world, killing nearly two million people so far, infecting tens of millions and eviscerating the global economy.

© Agence France-Presse