While this is good news for the city because it indicates that a large number of people have already been infected without becoming symptomatic, it makes the task of finding local test volunteers for the vaccine that much harder.
The institute has to harness 100 volunteers for the trial. Sources said that nearly 3,500 people have registered to participate in the trial, a little over 50% of them from other states.
“All participants have to undergo compulsory screening for pre-existing illnesses and Covid antibodies,” explained a doctor. “The screening of the first lot of volunteers from Delhi-NCR revealed that many of them already have antibodies against the coronavirus and are, therefore, ineligible for the trial.”
Selecting local people is important because it then becomes easier for AIIMS to monitor and manage any side effects of the volunteers.
A serological surveillance in Delhi recently revealed that 23.5% of the people had developed antibodies against Covid. Dr N K Mehra, emeritus scientist at Indian Council of Medical Research and former dean of AIIMS, told TOI that the actual number of people with antibodies could be even higher.
“It is important to exclude people who are already infected and have developed antibodies against because this is something the vaccine attempts to do,” Dr Mehra explained.
Vaccines contain the pathogens that cause the disease, and the Covid vaccine too has genetically engineered Covid-causing coronavirus.
According to the US Central for Disease Control and Prevention, a vaccine stimulates an individual’s immune system to produce antibodies, exactly like if that person was exposed to the disease.
“After getting vaccinated, you develop immunity to that disease without having got the disease,” the US health body said. “This is what makes vaccines such powerful medicine. Unlike medicines that treat or cure diseases, vaccines prevent them.”
However, if a person already has antibodies in his system against a particular virus, it would be difficult to assess whether the vaccine helped trigger an immune reaction.
Dr Mehra said ICMR was doing a great job in accelerating the research along with institutions such as AIIMS Delhi. “In India, we are exposed to higher microbial loads compared with western countries. That’s why our immunity is more robust. We have also been exposed to coronaviruses that cause common flu which may be giving some immunity against the new pathogen,” he added.