Covid-19 booster shot: How safe and effective is the mix-and-match third dose?

'Precaution dose' being given to senior citizens above 60 years and with co-morbidities, in Tamil Nadu. Image: ANI.

Indians, both residents or health workers, who are staying abroad and have been vaccinated twice, should get a booster or third dose in the country of their residence.

Why? 

There is still some confusion about its double usage. No one can quite say how taking two doses of Pfizer, or Sinivoc or Moderna will work with a Covishield or Covaxin, the vaccines being administered in India. 

``It is difficult to predict the outcome of mixing vaccines. My advice to those Indians living abroad, is to complete the booster or third dose in the country of their residence,” said Dr Samiran Panda, additional director general, ICMR.

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Apart from everything else, there is also the question of fitting an individual in the CoWin schedule, Dr Panda told Moneycontrol. 

CoWIN, the web portal for vaccine registration, which is owned and operated by the Union Health Ministry, currently lists only few of the approved vaccines. There is little clarity on when or whether the app/web portal will list the others. 

India started its booster-dose drive on January 10, covering frontline and healthcare workers, and senior citizens in the first phase.

Eight approved vaccines 

India has approved two new vaccines–Serum Institute of India's (SEI) Covovax and Biological E's Corbevax– expanding its programme amid a Third Wave fuelled by Omicron. Both have both been authorised for `restricted use in emergency situation’.

Read also: India should give booster shots to 18 to 60 year olds; it is the need of the hour

With the two new shots, India now has eight approved vaccines, three of which have been developed in the country.

The country is currently using only three–Covishield, Covaxin by Indian firm Bharat Biotech and Russian-made Sputnik V–for its vaccination drive. Of these, Covishield accounts for over 90 percent of the doses given so far. It has also approved ZyKoV-D vaccine–the world's first DNA vaccine against Covid– made by Indian firm Cadilla, but it's not available yet.

The Union government had also approved Johnson & Johnson's single-dose vaccine, which was to be introduced in India through a supply agreement with Biological E; and it had authorised Indian pharma company Cipla to import the Moderna vaccine. But it's unclear when either of those will be available in the country immediately.

It is also unclear if any of the newly approved vaccines will be deployed for booster shots.

Read also: Covaxin booster can neutralise Omicron, says Bharat Biotech

Is the cocktail vaccine safe?

Medical experts Moneycontrol spoke to did not express any safety concern with mixing-and-matching vaccines but weren’t sure about the 'mixed' booster dose’s effectiveness.

Rakesh Mishra, Director, Tata Institute for Genetics and Society (TIGS) told Moneycontrol: ``Studies are going on whether mixing vaccines are safe, and we will have conclusive results in the next couple of months, but I would say it is quite safe. One cannot say how effective it will be to mix two vaccines, but as far as safety is concerned, I don’t see any problem there.”  

Corbevax from Indian pharma company Biological E was developed in collaboration with US-based Dynavax and Baylor College of Medicine.

It is India's first indigenously developed recombinant protein sub-unit vaccine, Union health minister Mansukh Mandaviya told reporters. That is, it's made up of the coronavirus' `spike protein', which the virus uses to latch on and enter human cells. When injected, this sets off the body’s immune response.

Covovax is a local version of the Novavax vaccine and will be produced by the Serum Institute of India, which is also manufacturing Covishield or the Oxford-AstraZeneca jab.

The BBC quoted Dr Jeremy Kamil, a virologist at Louisiana State University Health Sciences Center in Shreveport, that it was imperative that the efficacy data of the vaccine `be vetted independently'. 

A former director of New Delhi’s premier AIIMS, Dr MC Mishra, however, believes much the same as TIGS’s Mishra, when he said that mixing vaccines is not an unsafe process, even if its effectiveness is under question.