The medical institute is to administer the vaccine to 100 people, who will be monitored for at least two weeks after getting the first shot. (Photo: REUTERS/Representational)

About 20% of those who expressed an interest in enrolling at AIIMS for clinical trials of India’s first indigenous Covid-19 vaccine, Covaxin, had already developed antibodies against coronavirus, making them unfit for the trials.

Sources said that two weeks after AIIMS began enrolling participants, the institute has screened more than 80 volunteers, but only 16 have been recruited. The medical institute is to administer the vaccine to 100 people, who will be monitored for at least two weeks after getting the first shot.

Those between 18 and 55 years of age with no heart, kidney, liver or lung illness and no uncontrolled diabetes or hypertension are eligible for the study. Routine investigations like liver, kidney function, Covid-19 detection, and rapid antibody tests are performed on volunteers before recruitment.

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“The rejection rate is very high as we can only recruit healthy volunteers. In almost 20% of the volunteers, we have found antibodies. This means they have already been infected. The remaining people do not have optimum liver or kidney function,” said a senior doctor at the hospital closely monitoring the trials.

Antibodies indicate a person is already infected with the virus and has recovered. “So, it is difficult to study the impact of the vaccine in them,” said the doctor.

The medical institute has received over 3,500 applications so far to participate in the human trials. On July 24, a 30-year-old male was administered the first dose of Covaxin. He was administered 0.5 ml through an intramuscular injection. “He has completed the first week and hasn’t reported any discomfort so far. We will monitor him till next Friday before administering the next dose of the vaccine,” said the doctor.

The country’s top medical institute is among the 12 sites selected by the ICMR for conducting Phase I and II randomised, double-blind (meaning neither the participants nor those delivering the vaccine know who is getting it) and placebo-controlled clinical trials of Covaxin. In phase I, the vaccine would be tested on 375 volunteers, of whom the highest, 100, would be at AIIMS. The second phase would include around 750 volunteers from all 12 sites put together.

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The vaccine has been developed by the Hyderabad-based pharmaceutical company Bharat Biotech in collaboration with the National Institute of Virology and Indian Council of Medical Research. The Drug Controller General of India earlier approved phase I and II human clinical trials.

A serological survey jointly carried out by the National Centre for Disease Control and state health authorities had recently reported a seropositivity rate of 22.86% for IgG antibodies on 21,387 samples randomly collected from across the 11