A study conducted by Sri Jayadeva Institute of Cardiovascular Sciences and Research has found Covid-19 antibodies were intact in 99% of the cohort, six months after they had taken both doses of Covishield.
Dr CN Manjunath, director, Jayadeva, said of the 250 fully vaccinated healthcare workers who were tested last week, in 99%, Covid antibodies were intact. He said this suggests booster doses are not required at this point in time.
The hospital’s department of microbiology had conducted blood tests for the IgG neutralising antibody via the Elisa method on 250 healthcare staff at the hospital including doctors and nurses. They all had received their second dose of Covishield in February this year.
The same batch of staff was tested for antibodies in April too, and 79% had shown a positive antibody response, while the remaining 21% had shown a negative immune response.
When the tests were repeated in September on the same cohort, a positive immune response was seen in 99% of them and only1% of these healthcare workers continued to show a negative immune response.
Taking into consideration the kits used for the study, a reference cut off value of 30% was considered a positive immune response.
In the September study, 49% of the cohort reported more than 90% antibody levels. The highest antibody response was seen among 19 healthcare workers who suffered a mild Covid-19 infection after being fully vaccinated.
Between April and September, only 10 healthcare workers showed a decline in antibody levels, but they still were within positive immune response limits, said researchers.
Delayed immune response
Dr Manjunath said the study has revealed the phenomenon of delayed immune response among some vaccine recipients.
“During antibody tests in April, 21% had not shown a positive immune response. When we repeated the tests four months later, we saw most of them developing positive antibody responses. This shows antibody response is not immediate in some individuals. They are called delayed immune responders,” said Dr Manjunath.
The study was spearheaded by Dr Naveena J, head of the department of microbiology, and the team included Dr MP Nandini and Dr K Kavitha, both assistant professors at the institute.
Jayadeva conducted the study to explore the need for booster vaccine doses for its staffers, who work in a highrisk environment and are therefore highly vulnerable to the infection. The study highlights the fact that two doses of Covishield at four-week intervals, is highly effective.
The fact that the immune response is intact after six months will have an impact on the booster dose vaccine policy.
“At six months, most vaccinated people do not require booster doses. However, we will have to subject the cohort to fresh antibody tests at the end of the year,” said Dr Manjunath.
He said the results of the study will help boost morale of healthcare workers as well as the general population and will also encourage more people to take the vaccine.