People with neutralising antibodies, however, may be able to handle subsequent infections better and with less morbidity.
Serosurveys are being conducted across India to find out the actual number of people infected with the novel coronavirus in the country. In a serosurvey, the blood serum of a group of individuals is tested for the presence of antibodies against that infection. This can indicate who has been infected in the past as most people who've recovered from COVID-19 have antibodies against the virus. But there's no strong evidence that people who have antibodies are protected against the disease or that recovered COVID-19 patients are safe from a second infection.
While antibody presence is a sign of previous exposure to the SARS-CoV-2, the virus that causes COVID-19, it may not always translate into protection against the disease, according to Indian scientists.
Immunologist Satyajit Rath from New Delhi's National Institute of Immunology (NII) told PTI that the presence of antibodies doesn't indicate anything about disease progression in people.
Vineeta Bal from Pune's Indian Institute of Science, Education and Research (IISER), also argued that though the presence of antibodies indicates the host's response to viral infection, they may not be able to stop further spread of the virus. Therefore, the simple presence of antibodies does not necessarily guarantee protection from COVID-19, the immunologist told the news agency.
Our body also produces neutralising antibodies (nAbs) against the novel coronavirus. This type of antibodies can block the entry of the virus into the host cell. According to Bal, the presence of nAbs in sufficient concentrations and for a longer period may give individual protection from second infection/exposure. But what levels of nAbs are 'protective' is not known clearly, she added.
Results of the serosurveys suggest that Covid-19 cases in the country are far more than actually reported. But the scientists noted that most of these surveys do not reveal antibody levels present in the blood. The tests identify people as just 'positive' or 'negative'.
A study published last month in JCI Insight, also noted that frequently used serology test may not detect antibodies that could confirm protection against reinfection of COVID-19. The most commonly used serological tests only indicate exposure to the virus, but they do not seem to suggest immunity to reinfection, it stated.
But there is no consensus yet whether the presence of enough nAbs will prevent reinfection. While some studies suggest that neutralising antibodies can protect people from COVID-19 reinfection, cases of reinfection have been reported from across the world.
But don't worry, reinfection does not mean you will become ill with Covid-19, according to Bal. Even though the presence of neutralising antibodies may not guarantee full protection against reinfection, a person with 'protective immunity' may be able to handle subsequent infections better and with less morbidity than otherwise, said Bal. She cited the recent case of reinfection in a person in Hong Kong. The person was discovered during a screening test but he didn't show any symptoms.
Scientists also not clear as to how long the antibodies persist in the body of the recovered patients. One study published in the NEJM journal claimed that antibodies against the new coronavirus remain in the body for four months after infection. Earlier evidence, however, suggested these important immune molecules disappear quickly.
