The WHO warns against the issuing of "immunity passports" that would allow people with SARS-CoV-2 antibodies to resume their activities or to travel. To date, there is no evidence that these people are immune to reinfection. The reliability of the tests is also in question.
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In a scientific brief from April 24th, 2020, the WHO reminded the policy and scientific community that the development of immunity is a multi-step process and often takes one to two weeks. The WHO also indicated specific stages in this process:
This dual-action can eliminate the virus from the body and, if the response is strong enough, prevent progression to severe disease or reinfection with the same virus. This process is usually measured by an antibody assay in the blood.
Most studies show that people have antibodies after infection. However, in some people, such antibody levels are very low. In addition, no studies have yet shown that the presence of antibodies to CoV-2-SARS is bulletproof protection against reinfection.
In fact, Prof. Peter Openshaw - a pulmonary immunologist and member of the UK government's New and Emerging Respiratory Virus Threats Advisory Group (NERTAG) - recently envisaged a "worst-case scenario": a partial resistance to the virus for only about three months. This scenario is based on current knowledge of the immunity acquired following infection with one of the four "benign" coronaviruses.
The WHO has made statements explaining that the accuracy and reliability of tests that detect SARS-CoV-2 antibodies in humans (especially rapid immunodiagnostic tests) still need to be further verified. Incorrect results, whether false positive or false negative, would impact efforts to control the pandemic.
These tests also need to be able to distinguish with certainty between infections caused by SARS-CoV-2 and those caused by other coronaviruses. In addition to the coronaviruses responsible for Middle Eastern Respiratory Syndrome (MERS-CoV) and ARDS (acute respiratory distress syndrome), four others cause the common cold and are widely circulating. People infected with one of these viruses can produce antibodies that react with those produced in response to SARS-CoV-2 infection.
Currently, such tests are widely used for screening purposes, both at the population level and for specific groups such as health care professionals. This helps to understand the extent of the infection and to identify associated risk factors. It is also a means of obtaining data on the percentage of people with detectable COVID-19 antibodies. However, most studies conducted in this setting are not designed to determine whether those tested are protected from re-infection.
The WHO, therefore, believes that the conditions are not yet in place for a reliable "immunity passport". Their use could even increase the risk of transmission: a person tested positive, thinking that he or she is definitively immune, could ignore public health recommendations.