Dr Arvind Lal, chairman and managing director, Dr Lal Path Labs, told TOI that his chain of diagnostic laboratories gets close to 400 such requests daily. Dr Navin Dang, founder and chairman, Dr Dang’s Lab, similarly said they get 20 to 30 requests for antibody tests from fully vaccinated persons every day.
At Apollo Hospital, group medical director Dr Anupam Sibal said numerous people sent queries about what the results of their antibody tests mean. “If the antibody levels are low, they go into a panic,” Sibal said.
Antibody tests, also called serology tests, look for antibodies in a blood sample to determine whether a person has had a previous infection. These are of two types: the qualitative one, which tells whether a person has antibodies against the virus or not, and the quantitative one which quantifies the antibody titres in the body. People mostly opt for the second one, the quantitative test, according to labs.
Different labs use different reference values to give the result of the antibody test. However, some of the labs claim that if the result is more than five times the reference value, say 67 units against a reference value of 12 units, it suggests good antibody levels.
“If the result is two to five times the reference value, it is suggestive of partial levels of antibody and anything less than two times the reference value is considered low,” said one diagnostic executive. Dr Jamal Yusuf, professor of cardiology at G B Pant Hospital, said many healthcare workers in that hospital have been found to have low antibody levels. “The antibodies wane over a period of time. This is why some of the countries have already started giving booster Covid doses,” Yusuf said.
According to Dr S K Sarin, vice-chancellor, Institute of Liver and Biliary Sciences, Vasant Kunj, 15-20% of the fully vaccinated people do not develop the desired levels of antibodies. “It is also true that the antibodies produced by vaccination wane over a period of time, say four to six months. But that does not mean that vaccines aren’t effective. We do not know for sure if the waning of antibodies levels makes a person vulnerable to infection as the T cell response of the vaccine remains effective for a long time,” he explained.
Apollo Hospital’s Dr Anupam Sibal said low antibody titres result doesn’t mean that the body will not mount an immune response when challenged by the coronavirus because humans have memory B cells and T cells that get activated and help fight the virus. The World Health Organization, US Food and Drug Administration and the Centre for Disease Control and Prevention have also advised against routine antibody testing to assess the protection from vaccines against Covid.