How Mixing Vaccines Could Help End India's Second-Dose Crunch

If trials find vaccine combinations are safe and effective, you will be able to follow up your first dose with a shot of any approved vaccine

- Anjishnu Das, Chethan Kumar

Is it safe to take shots of two different Covid vaccines? Are mixed vaccinations less or more protective? Several countries have begun trials to find out while the Indian government said it won’t change its vaccine protocols till mixed vaccinations are backed by science. If the trials succeed, you won’t need to delay your second dose just because a specific vaccine is not available.

Some countries have already allowed such ‘mix-and-match vaccinations in emergencies, with early trial results suggesting some combinations are safe and potentially more effective.

What mixing vaccines could look like

All approved vaccines, except Johnson & Johnson, need two doses. Generally, the first dose primes the immune system to recognise the virus and the second boosts the recognition and response to it.

Combining vaccines, say with a first dose of a viral vector vaccine-like Oxford-AstraZeneca’s Covishield and a second dose of an mRNA jab like Pfizer-BioNTech, is called ‘heterologous prime-boost’ and it could train the immune system to recognise the virus in more than one way.

Russia’s Sputnik V is a ‘combination’ vaccine by design. The first dose uses a harmless common cold adenovirus (Ad26) to deliver genetic instructions for cells to produce the coronavirus’s spike proteins. The second does it with a different adenovirus (Ad5), to avoid being attacked by the immune system that now recognises Ad26.