Why several countries considering mixing vaccines; what are possible benefits, side-effects

So far as the question of mixing vaccines arises, only few studies have been conducted on the issue and claims about increased efficacy on account of mixing doses are only good in theory at this point.

Amidst the shortage of Coronavirus vaccines and a large unvaccinated population India is seriously considering if mixed doses of two different vaccines could be administered. A scientific study is also soon going to be conducted to evaluate the efficacy of mixing separate Covid-19 vaccines and probable side-effects of the same, the Indian Express reported.

How will mixing vaccines help?
A section of scientists have said that mixing vaccines could make the fight against Covid-19 stronger as mixing doses of different vaccines results in production of a more potent immune response against the virus. Dr Chandrakant Lahariya, a senior vaccinologist told the Indian Express that mixing vaccines could prove more beneficial in case of viral vector vaccines like Covishield. Dr Lahariya explained that the effectiveness of such vaccines reduces substantially in successive doses as the body starts developing antibodies even against the adenovirus used by the vaccine.

Amidst concern over Coronavirus replicating into various strains and possibility of some Covid-19 vaccines proving ineffective against newer strains, scientists have highlighted that mixing vaccines could develop a wider and broad-range immune response against different mutations of the virus.

Amidst limited capability of vaccine manufacturers to supply vaccines across the country, it makes sense to allow mixing of vaccines. A large number of beneficiaries who have already received their first dose are facing constraints in getting the second dose of the same vaccine.

Need for cautious approach
Coronavirus vaccines in general are arguably the fastest developed vaccines in the world as clinical trials for vaccines against other diseases last for several years before they are given the final approval. However, in the wake of unprecedented misery and mortality caused by the pandemic, drug regulators across the world gave fast-track approvals.

So far as the question of mixing vaccines arises, only few studies have been conducted on the issue and claims about increased efficacy on account of mixing doses are only good in theory at this point. Studies on the issue also need to provide results to questions like which vaccines can be mixed and the duration between the two doses to mount an effective immune response against the disease.

Other challenges
Apart from the clinical impact of mixing vaccines on beneficiaries and probable side-effects, there are other logistical challenges that can pose a hurdle. For instance, the Coalition for Epidemic Preparedness Innovations has said that different vaccines can have different shelf life, varied storage conditions and unique shipping requirements.

A large number of currently-in-use vaccines have also not been tested in clinical trials for the purpose of mixing with other vaccines. Take for instance the indigenously developed Covaxin which has not been studied for the purpose of mixing in any study so far.

Which countries have allowed mixing Covid vaccines?
Among countries which have allowed mixing of Coronavirus vaccines are Canada, the United Kingdom and the European Union. These countries have allowed the beneficiaries who have already been jabbed by AstraZeneca vaccine to opt for Moderna or Pfizer vaccine as their second dose. Spain, South Korea, Russia and China are also conducting studies on the mixing of Coronavirus vaccines. The United States has also allowed the mixing of Pfizer and Moderna vaccines for beneficiaries only under exceptional circumstances.

Why mixing vaccines could prove beneficial in India
By the end of this year, the Indian government is expecting to get supplies of at least 7-8 kinds of Coronavirus vaccines developed using a range of technologies like viral vector, mRNA, DNA and recombinant protein among others. With the availability of 7-8 vaccines, a large number of studies of combinations of different pairs of vaccines could be undertaken in the country.