Study finds positive immune response in healthcare workers six months after vaccination

A study to assess the need for a booster dose of the COVID-19 vaccine taken up at the State-run Sri Jayadeva Institute of Cardiovascular Sciences in Bengaluru has found that 99% of a group of 250 healthcare workers, who received their second dose in February, showed positive antibody response even six months later.

Of the 250 healthcare workers, 20% were delayed responders. Initially, these 20% workers did not show a positive immune response in April when they took their first dose. Now, six months after their second dose (in February), they showed a significant improvement in antibody levels.

Institute director C.N. Manjunath told The Hindu that 19 (7.6%) of the healthcare workers, who were both COVID-19 infected and vaccinated, had shown the highest antibody responses. “Although 10 healthcare workers (4%) showed a decline in antibody levels from April to September, they still remain in the positive immune response limits of above 30,” he said. Doctors from the Department of Microbiology at the institute checked the robustness and longevity of anti-SARS-CoV-2 antibodies in the group. They conducted tests for IgG neutralising antibody levels by enzyme-linked immunosorbent assay or ELISA method. The group aged above 45 included 125 female health staff.

“We had tested the same group in April, two months after they had taken the second dose and had found a good antibody response in 80% of them. Our September study has shown good antibody response in 90% of them, which is very encouraging,” said Dr. Manjunath.


The employees had taken two doses of Covishield after an interval of four weeks as per the spacing rules then. “A majority of them had developed good immunogenic response then. After the government revised the gap between two doses to 12–16 weeks, there were doubts about immunogenicity among the healthcare workers who took the second dose after four weeks. Our study has cleared their doubts and also provided evidence that a booster shot may not be required,” the doctor said. “The findings can have a significant impact on the booster dose vaccine policy as at six months after the vaccination most people do not require a booster dose. However, we have to re-study this group at the end of one year,” he said.

Reduction in gap

Asserting that these results would boost the morale of the healthcare workers/general population and would also encourage more people to go for vaccination, Dr. Manjunath said he would submit the findings of the study to the ICMR as discussions on a booster dose were on. “Besides, this study also shows that it is scientific to reduce the gap between two doses of Covishield from 84 days (12 weeks) to 4–6 weeks,” the doctor said. “With the third wave anticipated in October–November, this community-immunity is likely to provide significant protection, provided there are no further mutations and people continue to follow COVID-19-appropriate behaviour,” he added.

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Sagar Biswas

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