The World Health Organization issued a warning that there is currently no evidence that people who recovered from the coronavirus and have antibodies in their blood plasma will be immune to the deadly virus, which suggests that people who have contracted the disease once might not be immune from being reinfected by the virus.

The WHO cautioned that serological tests, which look for the presence of antibodies in blood plasma, might not be as helpful in identifying immunity because there is no proof that humans can build up immunity to prevent being reinfected by COVID-19.

During a Friday news conference in Geneva, Dr. Maria Van Kerkhove said, "There are a lot of countries that are suggesting using rapid diagnostic serological tests to be able to capture what they think will be a measure of immunity. Right now, we have no evidence that the use of a serological test can show that an individual has immunity or is protected from reinfection."

"These antibody tests will be able to measure that level of seroprevalence - that level of antibodies - but that does not mean that somebody with antibodies means that they are immune," said Van Kerkhove, head of WHO's emerging diseases and zoonosis unit.

"What the use of these tests will do will measure the level of antibodies," Van Kerkhove said. "It's a response that the body has a week or two later after they've been infected with this virus."

Dr. Mike Ryan, executive director of WHO's emergencies program, noted that "nobody is sure" if humans with coronavirus antibodies could be reinfected.

"Nobody is sure whether someone with antibodies is fully protected against having the disease or being exposed again," Ryan said on Monday. "Plus some of the tests have issues with sensitivity. They may give a false negative result."

"With regards to recovery and then reinfection, I believe we do not have the answers to that. That is an unknown," Ryan said. "One would expect that a person who generates a full-blown immune response with detectable antibodies should have protection for a period of time. We just don't know what that period of time is."

Van Kerkhove referenced a preliminary study of the blood plasma of 175 patients in Shanghai who had recovered from the coronavirus.

"And that found some individuals had a strong antibody response," Van Kerkhove stated. "Whether that antibody response actually means immunity is a separate question. That's something that we really need to better understand is what does that antibody response look like in terms of immunity."

The Centers for Disease Control and Prevention rolled out a plan to do serologic testing in "more areas with high numbers of people with diagnosed infections." But the CDC also warned that "serologic test results have limitations that make them less than ideal tools for diagnosing people who are sick." The tests are "limited" because "it typically takes one to two weeks after someone becomes sick with COVID-19 for their body to make antibodies; some people may take longer to develop antibodies."

Professor John Newton, Director of Health Improvement at Public Health England, said the public should not use any unproven antibody tests.



"We are breaking new ground with this work every day, and I am confident this major research effort will make a breakthrough," Newton said. "Until then, please don't buy or take any unproven tests. They may not be reliable for your intended use; they may give a false reading and put you, your family or others at risk."

Over 582,000 people of the more than 2.2 million confirmed COVID-19 cases worldwide have recovered.







