Not all Covid recovered patients have antibodies, other aspects too important for recovery: Experts

New Delhi: While the second Serological survey of Delhi showed that 29.1 per cent of the population to have likely developed Coronavirus antibodies to fight COVID-19 — implying that they had been exposed to the virus, doctors and experts are now saying that not every COVID-19 patient is likely to develop antibodies after exposure.

According to a study conducted by the Kasturba Medical College, it said that 10 to 15 per cent of patients do not develop SARS-CoV-2 antibodies even after having contracted COVID-19. The reason experts believe this happens is that some patients might develop T-cell immunity, or a dominant IgA antibody response in respiratory mucosa and not a systemic IgG response to the virus.

Speaking to Millennium Post, Dr Richa Sareen, Pulmonology and Critical Care Medicine at Fortis Hospital said, "These cases are either the ones who are asymptomatic or mildly symptomatic. There are two types of immunity one is moral immunity which in simple words is antibody-mediated. Another is cellular immunity, where your body gets infected with the virus, there are certain cells that retain the memory (of the virus) and whenever you get re-infected, they attack that virus."

She said that moral immunity can be measured with antibody testing, but such deterministic tests are not available yet to ascertain cellular immunity "So, whether antibodies are developing or not we can just see the antibodies part of it, which till now the studies that have come up that people who are asymptomatic and people who are mild disease, not everybody is getting a good antibody count," Dr Sareen said.

Meanwhile, Dr Jatin Ahuja at the DM Infectious Diseases of the All India Institute of Medical Sciences (AIIMS) averred that getting antibodies is not always a fixed rule.

"People who are getting severe cases of COVID are found having a high number of antibodies compared to ones who have a mild infection," he said, adding that patients who have asymptomatic infections might be having immunity but not antibodies.

"Immunity that plays in our body is not just the antibodies. There is also G-immunity that plays a major role. But we are only concerned about the T-cell, which is an antibody response," Dr Ahuja said. He emphasised that it is not a thumb rule that antibodies are going to be generated always.

Dr Vivek Dixit, a senior scientist at AIIMS added that there is a possibility of re-infection as well with such weak antibody responses, adding that there are different antibodies in asymptomatics and those with severe cases. "But people who are asymptomatic, their condition can be seen in two ways, one is that their immune system is working great and second is that they had a little amount of viral load," he explained.

Meanwhile, the World Health Organisation also continues to review 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," a report by WHO had said.

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