The World Health Organization has warned there is no evidence to suggest the presence of antibodies in blood can determine whether someone has immunity to the coronavirus.
Dr. Mike Ryan, the WHO’s executive director for health emergencies, said Friday there was no indication so far that a large proportion of the population had developed immunity.
“There’s been an expectation, maybe, that herd immunity may have been achieved and that the majority of people in society may already have developed antibodies. I think the general evidence is pointing against that... so it may not solve the problem the governments are trying to solve.”
The number of recovered coronavirus patients who have retested positive for the virus has raised concerns about how antibodies work in response to Covid-19.
While scientists say there is no evidence yet that a person who has retested positive can spread the virus further, there haven’t been any conclusive studies to rule that out.
Professor Chris Dye, of the Oxford Martin School at Britain's University of Oxford, said substantial work to develop accurate antibody tests for coronavirus infection was ongoing.
“The WHO are right to highlight that any antibody test, if we get one, won’t be able to definitely say whether someone is immune to the infection, because we just don’t know enough yet about how immunity works with Covid-19," he told the Science Media Centre.
Such tests would need to be sensitive enough to ensure that infections were not missed, and specific enough to be confident that a positive result is correct, he said.
"Before an antibody test can be used to indicate that someone is immune to further infection, the level of protection must be demonstrated in experimental trials," Dye added.