WHO experts feel that at this point, there is not enough evidence about the effectiveness of antibody-mediated immunity to guarantee the accuracy of an “immunity passport” or “risk-free certificate.”
- WHO published a scientific paper on Friday on next phase of Covid-19 response
- Most WHO studies show people who recovered from coronavirus have antibodies
- Cellular immunity may also be critical for recovery, antibodies cant guarantee immunity
The World Health Organization (WHO) has published a new scientific paper for the next phase of Covid-19 response. It has noted the suggestions made by some governments to use the detection of antibodies of Covid-19 as the basis for an “immunity passport” or “risk-free certificate”.
Some experts had earlier suggested that in a post about Covid-19, individuals with antibodies should be able to travel and return to work assuming that they are protected against re-infection. The WHO has said that “there is currently no evidence that people who have recovered from Covid-19 and have antibodies are protected from a second infection”.
The scientific paper was published on Friday. The paper said, “Development of immunity to a pathogen through natural infection is a multi-step process that typically takes place over one to two weeks.”
The antibodies formed by human bodies in response to an infection are proteins called immunoglobulins. The body also makes T-cells that recognize and eliminate other cells infected with the virus. This process is called cellular immunity.
In most viral infections, when the combined adaptive response clears the virus from the body and “if the response is strong enough, it may prevent progression to severe illness or re-infection by the same virus”. The most common way to measure this response is to measure the presence of antibodies in blood.
The WHO has said that it continues to review the evidence on antibody responses to SARS-CoV-2 infection. Most of the studies monitored by the WHO show that people who have recovered from the 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.
“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 paper concluded.
The global health body has also said that the rapid immunodiagnostic tests, need further validation to determine their accuracy and reliability. “Inaccurate immunodiagnostic tests may falsely categorize people, they may falsely label people who have been infected as negative, and people who have not been infected are falsely labelled as positive.”
According to the WHO, both these errors have serious consequences and will affect control efforts. The tests also need to distinguish between past infections from the novel coronavirus and the six other human coronaviruses.
“Four of these viruses cause the common cold and circulate widely and the remaining two are the viruses that cause Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS),” the WHO said. People infected by any one of these viruses may produce antibodies that cross-react with antibodies produced in response to infection with the Covid-19 virus.
WHO experts feel that at this point, there is not enough evidence about the effectiveness of antibody-mediated immunity to guarantee the accuracy of an “immunity passport” or “risk-free certificate.” It has adviced people not to assume that they are immune to a second infection because they have received a positive test result in the past.