FAQ: Can I Take Second Dose of Covishield If I Don’t Get Covaxin?

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(Photo: The Quint)

With an acute shortage of COVID vaccines across the country, thousands of people above the age of 45 are missing their dates for the second dose.

While people are scrambling to get a slot, many are wondering if they can opt for an alternative if the vaccine from their first dose is not available in their city.

What do we know about mixing two vaccines? What is the science behind this? Here’s what we know till now.

I did not get a slot for Covaxin for my second dose. Can I take Covishield? Or vice-versa?

No, this is not recommended by the Ministry of Health and Family Welfare in India. As of now, you need to get two doses of the same vaccine – Covishield or Covaxin – to complete your vaccination cycle.

Is there a reason the two vaccines cannot be mixed?

First, no study concerning the mixing of the doses has been conducted in India.

Researchers say that not all vaccines work when they are mixed. Whether the mixed regimen, also known as a heterologous boost, works can be concluded only after scientific studies.

Do Covaxin and Covishield work differently?

Yes. The Oxford-AstraZeneca, or Serum Institute of India’s, Covishield, is a viral vector vaccine. The Bharat Biotech’s Covaxin is an inactivated vaccine. While the goal is the same, the vaccines use different mechanisms on the human body.

An inactivated vaccine or a ‘killed vaccine’ uses the ‘killed’ version of the pathogen that causes the disease. They are made from viruses or bacteria that have been ‘killed’ clinically and, therefore, cannot cause the diseases anymore, according to WHO. Covaxin, therefore, works like other inactivated vaccines, such as Hepatitis A, Influenza, Polio and Rabies.

Covishield, on the other hand, uses a modified version of a different virus as a tool to transport genetic material to a cell. It is “made from a weakened version of a common cold virus (known as an adenovirus) from chimpanzees. It has been modified to look more like coronavirus – although it can’t cause illness,” a BBC report explained.

Are other countries mixing vaccines?

Yes, predominantly the United Kingdom and France.

For example, in France, people who got the AstraZeneca vaccine for their first dose are being offered the vaccine developed by Pfizer and BioNTech SE for their second shot. This was after the AstraZeneca vaccine was restricted to older patients by the government.

In the United Kingdom, an ongoing study is experimenting with some people who got a first dose of AstraZeneca’s shot followed by Pfizer’s vaccine.

What did the study in the UK show?

According to the Lancet medical journal, those who took a mixed dose reported more short-lived side effects, most of them mild, researchers from the University of Oxford reported.

About 10 per cent of the 800 participants who got mixed doses reported severe fatigue, for instance, compared to about 3 per cent of those inoculated with a single type of vaccine, the ongoing research showed.

“Whether or not this will relate to an improved immune response, we don’t know yet; we’ll be finding out those results in a few weeks,” said Matthew Snape, an Oxford pediatrics and vaccinology professor, who’s leading the trial.

While all the participants in the study are aged 50 and above, it is possible that the reactions could be even stronger in younger patients, Snape added.