'6 months after jab, 99% show adequate immune response'

Six months after second jab, 99% still have adequate immune response: Study

The good immune response 6 months after the jab means that the booster can wait

 Representative image. Credit: iStock Photo

A whopping 99 per cent of 250 health workers jabbed with the Covishield vaccine in February at the Sri Jayadeva Institute of Cardiovascular Sciences and Research (SJICR) showed adequate immune response in September.

The good immune response six months after the jab means the booster can wait, especially since only 10 out of the 250 health workers showed a decline in antibody levels.

SJICR’s department of microbiology conducted the blood tests for IgG neutralising antibody levels by Elisa method on the 250 health workers who had received both doses of the Covishield vaccine by February.

There were an equal number of men and women among the health workers.

SJICR Director Dr C N Manjunath said around 80 per cent of the study group showed good antibody response when tested in April, two months after the jab.

When the tests were repeated on the same group in September, a much higher proportion — 99 per cent of the study group showed a positive antibody response.

As per the testing kits used, antibody levels of more than 30 per cent is considered as positive immune response.

Around 20 per cent of the workers who initially did not have a positive immune response in April have shown a significant improvement in antibody levels during September.

“They are called delayed responders. Out of these 250, around 19 health workers who were Covid-infected showed highest antibody responses. Only 10 health workers showed the decline in antibody levels from April to September, but still remained in the positive immune response limits of 4 per cent,” said Dr Manjunath.

“The study highlights the fact that two doses of Covid vaccines at four weeks interval is highly effective and the immune response is sustaining at six months, which will have an impact on the booster dose vaccine policy.

"At six months, most vaccinated people do not require the booster dose. We will restudy this group at the end of one year,” he added.

These results will boost the morale of the health workers and general population and might also encourage more people to go for vaccination.


“It is scientifically sound to reduce the second dose interval to four to six weeks from the existing 12 weeks.

"Since the third Covid-19 wave is anticipated during October-November 2021, this ‘community-immunity’ is going to have significant protection, provided there are no further mutations with continued Covid-appropriate behaviour,” he said.

Dr Manjunath credited the study to Assistant Professors Dr Naveena J, Head of the Department of Microbiology, along with Dr M P Nandini and Dr K Kavitha.

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