Covishield booster post Covaxin priming improves immune response 58x: CMC

Covishield fares significantly better as a booster or third shot after primary vaccination with either Covishield or Covaxin, shows a Christian Medical College Vellore study on heterologous vaccine boosting.

In an interview with Karan Thapar, Gagandeep Kang, microbiologist and professor at CMC Vellore, said that heterologous boosting with Covishield as a third shot after two doses of Covishield boosted antibody-led immune response by 58 times.

In an interview to The Wire, Kang said the findings of the study on mixing Covishield and Covaxin as the booster shot after one was primed with either two doses of Covishield or Covaxin would be published this week. The findings have been submitted to the government already.

They show that Covishield is a far more effective booster after two Covaxin jabs than the other way round. So far, India has not allowed heterologous boosting of vaccines. At present, those who have taken two doses of Covishield have to take its third shot. Likewise, for those who have taken Covaxin.

Kang said: “If you have had two doses of Covaxin, then you would have a better immune response with a third dose of Covishield, and also, if you have had two doses of Covishield, then you would have a better response with Covishield.”

Kang, a member of Britain’s Royal Society, confirmed the CMC Vellore study found out that a third Covaxin after two Covaxin increases antibodies six times but from a very low base; a third Covishield after two Covishield increase antibodies 6.8 times but from a very much higher base; whereas a third Covaxin after two Covishield only increases antibodies 2.5 times. A third Covishield after two Covaxin increases antibodies 58 times, the study has found.

The expert, however, also pointed out that while the Covaxin primed and Covishield boosted regimen starts to boost the antibody response from a lower bar, it has been found that people who have got Covaxin as primary dose and Covishield as booster end up with better immunity than those who have been Covishield primed, and Covaxin boosted.

Kang added that the CMC Vellore study was only testing responses of antibodies and not T-cells. She also pointed out that no tests were done using protein-based vaccines as boosters. The tests were limited to the two most widely used vaccines in India, Covishield and Covaxin.

In fact, she said, “We can boost the immune response of Covishield with protein vaccine heterologous vaccination.” She also added that this data is similar to the data from elsewhere in the world, which shows that if one has received an inactivated vaccine as their primary two doses then a vector or mRNA vaccine gives a better boost to immune response.

Also, the expert did not sound worried about people below 60 years and without any co-morbidities not getting a third shot of booster doses immediately.

“We know that a booster dose gives some incremental level of immunity. Most people below the age of 60 years and without any co-morbidities, do they really need a booster? Nowhere in the world there is evidence that a public health programme is boosting people under the age of 60 years within the time frame that we have done, or others in the world may have done. I think we have been in a rush to provide protection against a pandemic and we may have given too many doses too soon in some cases,” she said in the interview.

She felt that the time had come to redefine what we mean by a wave, by not focusing on tests and their outcomes but on how serious the disease is and the number of deaths.