No evidence yet that people who have recovered from coronavirus cannot be reinfected, warns WHO
The World Health Organization (WHO) has warned that there is currently “no evidence” that people who have recovered from COVID-19 and have antibodies are protected from a second coronavirus infection. Accordingly, the experts have warned countries against issuing “risk-free certificate” or “immunity passport” to people who have been infected - on the assumption they would be immune to reinfection - as their accuracy cannot be guaranteed
“WHO has published guidance on adjusting public health and social measures for the next phase of the COVID-19 response. Some governments have suggested that the detection of antibodies to the SARS-CoV-2, the virus that causes COVID-19, could serve as the basis for an immunity passport or risk-free certificate that would enable individuals to travel or to return to work assuming that they are protected against re-infection. There is currently no evidence that people who have recovered from COVID-19 and have antibodies are protected from a second infection,” says a scientific brief issued by the WHO.
Many countries are now testing for SARS-CoV-2 antibodies SARS-CoV-2 antibodiesat the population level or in specific groups, such as health workers, close contacts of known cases, or within households. The studies are critical for understanding the extent of and risk factors associated with infection. These studies will provide data on the percentage of people with detectable COVID-19 antibodies, but most are not designed to determine whether those people are immune to secondary infections, says the WHO.
The experts say that at this point in the COVID-19 pandemic, there is not enough evidence about the effectiveness of antibody-mediated immunity to guarantee the accuracy of an immunity passport. The WHO cautions that people who assume that they are immune to a second infection because they have received a positive test result may ignore public health advice. “The use of such certificates may, therefore, increase the risks of continued transmission. As new evidence becomes available, WHO will update this scientific brief,” says the statement.
As of April 26, over 2,897,640 COVID-19 cases have been reported globally, and 202,880 have died in the coronavirus pandemic, shows the Johns Hopkins tracker.
According to the experts, the development of immunity to a pathogen through natural infection is a multi-step process that typically takes place over one to two weeks.
“The body responds to a viral infection immediately with a non-specific innate response in which macrophages, neutrophils, and dendritic cells slow the progress of the virus and may even prevent it from causing symptoms. This non-specific response is followed by an adaptive response where the body makes antibodies that specifically bind to the virus,” explains the WHO.
It further says, “These antibodies are proteins called immunoglobulins. The body also makes T-cells that recognize and eliminate other cells infected with the virus. This is called cellular immunity. This combined adaptive response may clear the virus from the body, and if the response is strong enough, may prevent progression to severe illness or re-infection by the same virus. This process is often measured by the presence of antibodies in the blood.”
The WHO is currently reviewing the evidence on antibody responses to SARS-CoV-2 infection. Most of these studies show that people who have recovered from infection have antibodies to the virus. However, some of these people have very low levels of neutralizing antibodies in their blood, suggesting that cellular immunity may also be critical for recovery, says the WHO. As of April 24, no study has evaluated whether the presence of antibodies to SARS-CoV-2 “confers immunity to subsequent infection by this virus in humans,” the WHO cautions.
“Laboratory tests that detect antibodies to SARS-CoV-2 in people, including rapid immunodiagnostic tests, need further validation to determine their accuracy and reliability. Inaccurate immunodiagnostic tests may falsely categorize people in two ways. The first is that they may falsely label people who have been infected as negative, and the second is that people who have not been infected are falsely labeled as positive. Both errors have serious consequences and will affect control efforts,” says the WHO.