The Indian Council of Medical Research (ICMR) study on the effectiveness of mixing and matching of vaccine doses is not enough to make a case for heterologous vaccination, according to Dr Sanjay Rai, a Senior Epidemiologist and Professor at the Centre for Community Medicine at AIIMS, New Delhi. Rai told BusinessLine, 98 people cannot represent the whole population, so the ICMR study cannot be taken as scientific evidence. These vaccines are new and it is critical to observe their efficacy in the long run. If mixing is allowed so soon, then the process of monitoring any adverse side effects of the current vaccines will get hampered. It is to be noted that Christian Medical College (CMC), Vellore is also conducting a study on the mix and match of doses, and has sought a review of its early findings by the regulator.

“Currently, 33 vaccines have been approved by (global) regulatory authorities for Covid-19. Few vaccine manufacturers are using completely new technology such as mRNA or DNA technology. We do not have any evidence of long-term effects of these vaccines,” Rai added.

Uncertainty prevails

“From the scientific point of view, mixing should not be allowed, because we never know if the results will be good or bad. No one can be held accountable if any mishappening occurs in future due to any vaccine. Some vaccines are causing blood clotting, some are causing pericardial effusion and others are triggering myocarditis,” said Rai. He added that the duration of protection also varies from vaccine to vaccine.

“Also, some vaccines are giving protection for six months and some are protecting for a year. So we don’t know the duration of protection and the overall shield they can provide. The long term harm can’t be monitored if mixing is allowed and nobody can be held accountable in such a scenario,” Rai added. “We should not allow mix and match now. Few pharma companies want heterologous combinations for inoculation because then, no one will be able to prove which vaccine harmed and which was safe,” he alleged. He stressed that it is unethical to allow mixing at this point in time when there is not enough data to prove their effectiveness.

Neutralising antibodies

According to Rai, measuring antibodies is not enough while deciding on mixing of vaccines. In case, a new variant emerges, Rai elaborates, these vaccines may not be able to elicit enough neutralising antibodies. Neutralising antibodies are small immune proteins known for their ability to actively neutralise invading pathogens. He said that in Omicron, it was seen that the antibodies proved to be ineffective and the spike protein mutated considerably.

Rai’s observations come even as Health Ministry officials maintain that a policy decision on mixing and matching of booster doses will be based on scientific evidence. So far more than 180 crore doses have been administered in the country out of which more than 149 crore are Covishield and 29.85 crore are Covaxin shots.

As of now, only three vaccines — Covaxin, Covishied and Sputnik V — have been used in the country. Out of these three vaccines, more than 85 per cent of the people in the country have received Covishield doses. Meanwhile, Biological E and Zydus Cadila have delivered 5 crore and 1 crore doses respectively to the Government but not a single shot has been administered so far, as per sources.

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