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What Happens if You Mix Covishield & Covaxin? Experts Say No Data

COVID Vaccine: “This is clearly a mistake. Simply because we don’t know about it’s efficacy,” Dr Rakesh Mishra said.

Updated
COVID-19
4 min read
COVID: There is no reason to expect any awful consequences from “mixing” vaccines, experts said.
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The government may soon start studies on the feasibility of mixing doses of two different COVID-19 vaccines, something which several countries around the world have already started testing, reports say.

What happens if you mix COVID vaccines — take the first dose of one vaccine and the second dose of a different one? While the efficacy and safety of mix-and-match COVID vaccines is still being studied in some countries, there has been growing concerns in India after a group of Uttar Pradesh villagers were given mixed doses of Covishield and Covaxin earlier this month.

All the experts FIT spoke to said there are no likely major concerns about the actual safety and side effects of the goof-up. But, this still can’t be condoned as no studies have been done to test the combo doses.

The Centre in a press briefing also said significant adverse effects are “unlikely” if an individual's second Covid vaccine dose is different from the first.

“We will have to wait for more scientific understanding of this for scrutiny and more understanding. But even if this has happened, it should not be a cause for concern for that individual.”
Dr VK Paul, Chair of NEGVAC (National Expert Group on Vaccine Administration for COVID-19)

But will the mixed combination work? Will it work as well as the original vaccines? Will it work even better? Here are the answers.

An ‘Awkward Mix’, But What of Efficacy?

“It's an awkward mix!” eminent Immunologist Dr Satyajit Rath said, adding that however, there is no reason to expect any awful consequences from this “mixing”.

“Vaccine are not medications, instead they actually evoke targeted responses from the body. Mixing vaccines usually does not cause any problems. We do after all give many vaccines together to infants in the childhood immunisation programme.”
Dr Satyajit Rath, Immunologist

Dr Rakesh Mishra, former director and now advisor of the Center for Cellular and Molecular Biology (CCMB) said this is not a “disaster” and that it’s not “harmful”. However, he cautions.

“Mixing of vaccines is normally not permitted. So, this is clearly a mistake. Simply because we don’t know about it’s efficacy,” Dr Mishra said.

If It’s Not Harmful, Why Is Mixing Vaccines Still a Problem?

Experts say it is something that should have been avoided since we don't know the outcome and have no data to support it. Hence, it could become a confusing situation over what protocol to follow.

Eminent virologist Dr T Jacob John said it should not have happened as there are no studies on mixing COVID vaccines. It's the moral responsibility of the government to address it, he said.

Dr Rath thinks it is incorrect, as a matter of proper process, to give any such combination that has not been approved by the regulatory system.

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“I am deeply concerned that we should not be using a process (or even letting it happen inadvertently) in the absence of evidence and regulatory approvals, both of which are completely lacking about this ‘mixing’.”
Dr Satyajit Rath, Immunologist

Dr Mishra says we should not experiment with the vaccine protocol. “What has been standardized is based on the trial results that are done…whether it is the dose of the vaccine or the gap between the two doses. Otherwise, we cannot get the best results that we know of.”

Will the Mixed Combination Work Well?

The short answer to all these questions, according to experts is, “We don't know.” This is because no trials have been done so far.

“My guess is that the mixed regimen will also provide reasonable protection, but we should not be using it in the absence of evidence and regulatory approvals,” Dr Rath said.

According to Dr Mishra, the worst case scenario is that since both vaccines are of single dose, one would have to wait for sometime to get the second dose of the ‘mixed-up’ vaccine in a few months.

“The best case scenario may be the first dose of one vaccine and the second dose of the other vaccine may be even better. Most likely in real life it will be something in between this,” Dr Mishra said.

While it is not a harmful situation and is certainly better than no vaccination, it probably will not be as good as being fully-vaccinated with proper dose of the vaccines.

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Weighing ‘Mix And Match’ for India

A lot of countries are looking at switching to different COVID vaccines for second doses owing to supply delays and safety concerns.

A recent study in Spain found that vaccinating people with both the Oxford–AstraZeneca and Pfizer–BioNTech COVID vaccines produces a strong immune response against the virus.

Several European countries are recommending that people who were given a first dose of the AstraZeneca vaccine get another vaccine for their second dose.

Should India, which is facing huge crunch in vaccines, also consider mix-and-match actively? Experts say “No”.

“No, I will not suggest mixing of vaccines because of the shortage. That should be done on scientific data. You can’t be playing with it. Deliberately doing these things because of shortage is not good,” Dr Mishra said.

Dr Rath said, “If we had, globally, decided that we will treat COVID-19 vaccines as a public health issue to be handled by representative governments in the public good, rather than as an unfettered arena for private companies to compete with each other in, we could have insisted on the development of public-sector comparative trials, like the WHO proposal for a solidarity vaccine trial last year that never got any traction.”

This way we would have had good reliable evidence-based answers to many such questions including the strengths and limitations of vaccine mixing, he said, adding it is still not too late.

(This story was first published on FIT and has been republished here with permission.)

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