The World Health Organization (WHO) said there is currently no evidence that people who have recovered from #COVID19 and have antibodies are protected from a second infection. WHO has published guidelines on the improvement of public health and social interventions for the next phase of the COVID-19 response. Some governments have proposed that the identification of SARS-CoV-2 antibodies, a virus that causes COVID-19, could serve as the basis for a “immunity passport” or a “risk-free certificate” that would allow individuals to travel or return to work on the presumption that they are safe from re-infection. There is currently no proof that people who have recovered from COVID-19 and have antibodies are safe against a second infection.
Until a few days ago, it was believed that people infected with the corona virus were likely to develop antibodies that could attack the virus to avert the risk of re-infection. Based on this, corona is being treated with plasma therapy worldwide. In India too, in many states including Kerala, Delhi, Rajasthan, the infected patients are being given plasma with antibodies.
The development of immunity to pathogens through natural infection is a multi-step process that usually lasts for 1-2 weeks. The body responds immediately to a viral infection with a non-specific innate response in which macrophages, neutrophils and dendritic cells delay the progression of the virus and may also prevent symptoms from occurring. Following this non-specific reaction is an adaptive response, where the body generates antibodies that directly bind to the virus.
Such antibodies are also immunoglobulins proteins. The body also produces T-cells which recognize other cells infected with the virus and remove it. This is known as cellular immunity. A combined adaptive response can clear the virus from the body and can avoid relapse of serious illness or re-infection by the same virus if the response is effective enough. This cycle is also measured by the production of blood-borne antibodies.
WHO continues to study evidence about antibody responses to infection with SARS-CoV-2. Many of these findings indicate that people suffering from infection have antibodies to the virus. Some of these men, however, have very low levels of antibodies neutralizing in their blood, indicating that cellular immunity can also be important for recovery. Whether the presence of antibodies to SARS-CoV-2 provides immunity to subsequent infection with this virus in humans has not yet been evaluated.
Laboratory studies that detect SARS-CoV-2 antibodies in humans, including rapid immunodiagnostic studies, require further testing to determine their accuracy and reliability. Inaccurate immunodiagnostic tests can misclassify people in two ways. The first is that people who have been infected may be falsely labeled as negative and the second is that people who have not been infected are falsely labeled as positive. Both mistakes have significant repercussions and will hinder monitoring efforts. Such tests will also differentiate exactly between past SARS-CoV-2 infections and those caused by the known collection of six human coronaviruses. Four of these viruses triggers the common cold, and are widely circulating. The remaining two are the viruses that cause respiratory syndrome in the Middle East, and extreme acute respiratory syndrome. People infected with any of these viruses that produce anticorps that interfere with antibodies generated in response to SARS-CoV-2 infection.
Many countries are now testing at population level or in different groups for SARS-CoV-2 antibodies, such as health staff, near contacts with reported cases, or within households. WHO supports these research, as they are crucial to understanding the nature of infection – and the related risk factors. Such studies will include data on the percentage of individuals with detectable COVID-19 antibodies, but most are not planned to assess if certain individuals are resistant to secondary infections.
There is insufficient evidence at this point in the pandemic about the efficacy of antibody-mediated immunity to guarantee the accuracy of a “immunity passport” or “risk-free certificate.” People who believe they are immune to a second infection because they have received a positive test result may disregard advice from the public health. Therefore the use of these certificates will increase the risk of continued transmission.
