The World Health Organization's top emergencies expert Mike Ryans told a briefing on Friday that even if antibodies were effective there was little sign that large numbers of people had developed them and were beginning to offer so-called "herd immunity" to the broader population.
"A lot of preliminary information coming to us right now would suggest quite a low percentage of population have seroconverted (to produce antibodies)," Ryans said.
"The expectation that ... the majority in society may have developed antibodies, the general evidence is pointing against that, so it may not solve the problem of governments." The World Health Organization is also not sure whether the presence of antibodies in blood gives full protection against reinfection with the new coronavirus.
World Health Organization epidemiologist Maria van Kerkhove also said at the briefing that a sharp upward revision in China's coronavirus death toll on Friday was "an attempt to leave no case undocumented." Kerkhove said the Chinese authorities had gone back over data from funeral services, care homes, fever clinics, hospitals and detention centers, as well as the number of patients who had died at home, in the city of Wuhan, source of the coronavirus outbreak.
