MIXING COVID VACCINES

MIXING COVID VACCINES

Subject: Science & tech

Context : India plans to embark soon on an exercise to investigate if it can immunise people using a “mix and match” of different Covid-19 vaccines.

Concept :

• This would mean following up one dose of a particular vaccine with a second dose of a different vaccine. In scientific terms, this is called “heterologous” immunisation.
• In India, whose vaccination programme currently uses Covishield, Covaxin and Sputnik V, this practice has not been approved yet. Other countries have already been testing this out.

Why mix and match Covid-19 vaccines?

• BETTER IMMUNE RESPONSE: Some scientists believe that using a different vaccine for the second dose could potentially boost the immune response against the virus. This may especially be true for viral vector vaccines like Covishield/AstraZeneca, which use a modified and weakened chimpanzee ‘adenovirus’ (common cold virus) to deliver the genetic code of the SARS-CoV-2 spike protein to the body.
• MUTATIONS & VARIANTS: Mixing and matching vaccines of different technologies — for example, a viral vector vaccine followed up with an mRNA vaccine like Pfizer’s — might encourage our immune system to build a wider response.
• SHORTAGES IN SUPPLY: Current Covid vaccine production cannot sufficiently cater to the existing demand, resulting in stock-outs. In parts of India, government vaccination centres for those in the 18-44 age group had closed down due to limited Covishield and Covaxin supplies.
• SAFETY CONCERNS: Countries like Germany, France, the UK and Canada have halted the use of the AstraZeneca vaccine in younger age groups due to concerns of rare blood clot.

Concerns

• UNTESTED COMBINATIONS: Some vaccines like Covaxin have not even been administered in a mix and match scenario
• DIFFERENCES IN VACCINES: International bodies like the Coalition for Epidemic Preparedness Innovations, which is looking into mixing and matching Covid-19 vaccines, have highlighted certain complexities.
• SIDE EFFECTS: Studies such as the Com-COV trials show that some combinations, like AstraZeneca with Pfizer vaccines, could lead to an increase in side effects.
• THE SILVER LINING: As of now, there are no issues theoretically that could make mixing and matching of Covid-19 vaccines a major safety threat.