The ' precaution’ dose that is scheduled to be available to healthcare workers, frontline workers and those over 60 with co-morbidities may not necessarily be a repeat dose, senior Union Health Ministry officials said on Thursday.
“A decision will be taken this week. The NTAGI as well as other bodies are assessing the available data on the safety and efficacy of all the vaccines globally and there are meetings everyday. Before January 10, we’ll have a set of clearcut guidelines on what the recommended vaccine would be,” said Director General, Indian Council of Medical Research (ICMR) Balram Bhargava at press briefing.
The debate on third doses comes amidst a surge in infections in India that has seen cases cross 10,000 a day with State governments suggesting that they are being led by the Omicron variant.
Registrations for booster doses and Covaxin — the only option now — for those 15-17 is set to commence next according to guidelines issued by the Health Ministry this week.
A key factor under consideration is also the intended recipients as well as the supply of the vaccine, Dr .Bhargava added. The way the vaccine expansion programme is planned is that only those with a 39-week gap (9 months) following their second dose would be eligible for their precaution dose.
India has approved , under emergency use authorisation, Covishield, Covaxin, Sputnik V, Corbevax and Covavax. When the vaccination programme began in January 2020, the vaccine was only made available to healthcare workers, later frontline workers and then those over 45. A sizeable number of them were administered Covaxin in the early days of the vaccination programme though as the drive was opened up, Covishield became the most widely used vaccine because of availability.
While two doses of a vaccine are believed to be effective at priming the immune system to stave off disease and death, antibody levels — that typically fall after a few months — must be high to improve chances of avoiding symptomatic infection. However, no studies so far have determined the minimum level of antibodies required to prevent infection.
The definitive study so far on booster doses is the COV-BOOST study, led by the University of Southampton in the United Kingdom that tested seven different vaccines as a booster dose in groups of those who had received either two doses of the Oxford vaccine (Covishield) or the Pfizer vaccine. The third dose was administered at least 70-84 days after the second shot. The second shots were either of Novavax (same as Covavax), Valneva (an inactivated whole virion similar to Covaxin), Janssen, Moderna, Curevac or repeat doses of either Pfizer or Oxford vaccine. The overall conclusion of the study was that while all combinations boosted antibody levels, the increase was highest for Moderna as a third dose. The inactivated vaccine induced the least spikes. Were the mRNA vaccines to be excluded, as India doesn’t have them yet, Novovax induced a much greater spike in antibodies after the mRNA vaccines. Antibody levels alone weren't the sole metric of comparison as the trial also noted instances of adverse reaction or post-immunisation side effects.
Covaxin has not been tested anywhere as a booster except during an accidental mixup during a vaccination drive earlier this year when some recipients got a second dose of Covaxin instead of Covishield. An analysis suggested that this was safe and in fact boosted their antibody levels higher than two doses of the same vaccine. The Christian Medical College, Vellore is in the middle of a trial to evaluate Covaxin and Covishield as third doses.
There is also no trial that has evaluated Corbevax as a booster dose.
Dr. Bhargava said at the briefing that the available evidence from international studies and India so far suggested that immunity from disease from following vaccination or an infection lasted for about nine months.