A booster dose with a COVID-19 vaccine different from the one used for the first immunisation raised antibody levels more than a booster with the same vaccine.
A Covishield booster following a two-dose Covaxin immunisation gave the highest antibody response, compared with a Covaxin booster following two Covishield shots, but these levels, on their own, were no guarantee against protection from a future Omicron infection, Jayprakash Muliyil, member of the National Technical Advisory Group on Immunisation (NTAGI), told The Hindu.
Dr. Mulayil was commenting on headline results from a study conducted by the Christian Medical College, Vellore, and commissioned by the Centre to garner evidence on the way ahead for India’s vaccination policy. So far, India has administered more than 191 crore vaccine doses, with nearly 90% of the adults receiving at least one dose. The NTAGI peruses data on vaccination and is one of the expert scientific bodies that recommends approved vaccines for public administration.
Scientists from the CMC conducted the study on 400 patients, who were given different combinations of Covishield or Covaxin as heterologous or homologous boosters. They presented their findings to the NTAGI as well as the Drugs Controller General of India.
A heterologous booster is when the third dose is different from the earlier doses. A detailed report on the findings of the study is expected in the coming fortnight, according to a person privy to the study who declined to be identified. This person too confirmed that antibody numbers from a heterologous booster were higher.
“Every combination, homologous and heterologous, boosted antibody levels. Covishield followed by two Covaxin was most impressive (in levels) and three Covaxin doses gave the least response but that by itself is not the whole story and only shows that the body’s T cells (immunity cells) recognise the virus and produce a response,” Dr. Muliyil, a former principal of the CMC, said.
“The Omicron-led wave, as studies from England have shown, significantly boosted antibody levels. So the antibody levels in people following an Omicron infection is substantially high and booster doses aren’t really adding to it.” ‘
He added that the CMC study was commissioned before the Omicron wave, but now, following the wave, it had “limited importance”.
He said that there was no scientific evidence to show that vaccinations would not benefit children because they were being “vaccinated by Omicron”. This was because children, the evidence showed, manifested only a mild infection and Omicron being a SARS-CoV-2 variant that induced a high antibody response on infection, a vaccine dose would unlikely be significantly beneficial.
The NTAGI hasn’t recommended any vaccine for children below 12.
That the heterologous boosts provoke a greater immune response than a homologous boost has been borne out by several studies from across the world. India is currently following a policy of homologous boosters.
Following a recommendation from the NTAGI, Indian citizens and students travelling overseas can now take the precautionary dose of COVID-19 vaccine as required by the guidelines of the destination country, Union Health Minister Mansukh Mandaviya said in a tweet on Thursday.
On April 10, India began administering precautionary doses to all aged above 18 at private vaccination centres. Both Covishield, manufactured by the Serum Institute of India, and Bharat Biotech’s Covaxin are available for ₹225 per dose, down from ₹600 and ₹1,200, respectively. Private vaccination centres can charge up to ₹150 per dose as service charge over and above the cost of the vaccine.
With overall case numbers low, the precaution dose numbers have been low in India with a little over 1,00,000 doses being administered daily.
