Reasons to mix two different vaccines of COVID-19 or not

In India, couple of vaccines is being used at the moment. Both the vaccines have come from the brand Covaxin and Covishield. Through new ICMR study, it had been found out that two different vaccines of COVID-19 such as Covaxin and Covishield can be mixed together to offer better immunity. However, different platforms of delivering the vaccine are used by Covaxin and Covishield. By Covishield, adenovirus vector platform can be used while Covaxin uses the inactive virus.

Studies are being conducted to know whether a mix of two vaccines is more effective than two doses of the same vaccine. However, vaccine should not be mixed randomly. Looking at multiple issues, measures must be taken on the occasion

Participants of ICMR Study

Due to a mistake, the study has started in the first places. In one of the villages of Uttar Pradesh, 18 villagers have been given Covaxin for second dose whereas they have been administered Covishield six weeks ago. The study has said “Overall, this study demonstrates that immunisation with a heterologous combination of an adenovirus vector platform-based vaccine followed by an inactivated whole virus vaccine is safe and elicits better immunogenicity than two doses of homologous vaccination, using the same vaccines.” The study has been in the pre-print format till now and it is not peer viewed yet.

The Finding explains

Dr. Vineeta Bal, a leading immunologists has said “While ICMR using a mistake to get some preliminary data on heterologous vaccination is commendable, there is no great novelty in the approach. These results are really preliminary because it examines only 18 individuals with mixed vaccination.” Later on, she has also added “There is no easy immunological explanation in the present case… The data shows that heterologous vaccination triggers better antibody response as compared to two shots of Covaxin. However, there is no such enhancement seen with two shots of Covishield.”

One of the prominent vaccine scientists, Dr Gagandeep Kang has said “Theoretically we can provide some explanation, but there is no data to state whether it is equally immunogenic or in some cases more immunogenic to use a combination of vaccine doses via a vis others.”

Can we mix the vaccine?

World Health Organization has said that there is very less data regarding immunogenicity or effectiveness of mixing vaccine. Recommendation from the AstraZeneca has been modified on the occasion as it has been said following to an mRNA vaccine for the first dose of AstraZeneca, same type of vaccines should be used only. Through an email, WHO has explained “WHO is of the view that the mix-and-match regimens are likely to work. However, we really need to analyse the evidence in each of these vaccine combinations before any other recommendations can be made”

Through a regulatory viewpoint, Dr. Kang has said “Under their purview as applications from companies, because companies want to sell two doses of their product, not one in combination with another company’s product. When academics do studies, they want to characterise immune response and understand whether it is strong and long lasting. All this is a process of learning and we have a long way to go and not just take limited information and draw large inferences.”

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