GENEVA -- It is unclear whether patients who have recovered from COVID-19 are immune to further infection, the World Health Organization said on Monday, as they may not develop sufficient antibodies to resist the virus the next time it enters their body. If the number of people with immunity to coronavirus is limited, it may mean a delay in lifting lockdown restrictions and social distancing guidelines.
Some members of a recent study in Shanghai showed "no detectable antibody response," while others showed a very high response, said Maria Van Kerkhove, an infectious disease expert at the WHO. If a person develops only a small number of antibodies, they may once again test positive for the virus. In South Korea, 111 people have been diagnosed as positive after recovering once.
Van Kerkhove added that more information from patients who have recovered is needed, and indicated the WHO is hurrying to collect more data to analyze.
It is unclear whether the virus has reactivated in patients that test positive after recovery, or if they have suffered a new infection. "With regards to recovery and then reinfection, I believe we do not have the answers for that," said Mike Ryan, head of emergency response at the WHO. "That is unknown." He added that it is unclear how long the antibodies remain effective.
When humans are subject to infection, they generally develop antibodies that create immunity, meaning it is difficult for them to be infected by the same disease again.
The U.S. and European countries will now start widespread antibody testing. They plan to check whether patients gain immunity to the coronavirus after infection.
In Italy, where more than 20,000 people have died from the virus, authorities have already begun testing in the northern region. The National Institute of Health in the U.S. will also collect blood samples from up to 10,000 people across the country to test for antibodies and check for a history of infection.
Some countries in Europe have imposed strict restrictions on people leaving their homes, and many believe their infections have peaked for the time being. Some of those countries are now preparing to lift those restrictions.
Countries are now testing for antibodies, because if immunity is confirmed it will make the decision to lift social distancing restrictions much easier. Ending those will be one of the first steps in getting economic activity up and running again.
But the fact that some in South Korea and Japan have tested positive again, even after recovering from the virus, has raised the possibility that the body may not produce sufficient antibodies to develop immunity after infection. A good deal is still unknown about the coronavirus itself. The WHO has warned that the risk of reinfection is high if countries loosen social distancing restrictions too quickly.
"While COVID-19 accelerates very fast, it decelerates much more slowly," said WHO Director-General Tedros Adhanom Ghebreyesus at a press conference on Monday, meaning control measures need to be lifted slowly. He warned that the fatality rate of the coronavirus is 10 times higher than the H1N1 strain of influenza that hit the world in 2009.