Mixing Covid-19 vaccines: Benefits and Concerns

What is the news?

India plans to conduct research on Mixing Covid-19 vaccines. This is to investigate if it can immunize people using a “mix and match” of different Covid-19 vaccines.

What does mixing of vaccines mean?
  • Mixing of vaccines means following up one dose of a particular vaccine with a second dose of a different vaccine. In scientific terms, this is called “heterologous” immunization.
Have vaccines been mixed before Covid-19?
  • Mixing and matching of vaccines have been tested for decades, especially for viruses like Ebola. However, most combinations had initially been restricted to vaccines that use the same technology.
  • In India, combinations of rotavirus vaccines have also been used and tested out.
Reasons for mixing Covid-19 vaccines:
  • Better Immune Response: Several scientists believe that using a different vaccine for the second dose could potentially boost the immune response against the virus.
    • Example: Viral vector vaccines like Covishield use a modified and weakened chimpanzee ‘adenovirus’ (common cold virus). But using the same adenovirus could make the vaccine less effective the second or third time around. That is why Sputnik V uses two different adenoviruses to deliver the spike protein’s code to our bodies.
  • Protection against mutations and variants: Mixing and matching vaccines of different technologies such as a viral vector vaccine followed up with an mRNA vaccine-like Pfizer’s might encourage our immune system to build a wider response.
    • Such combinations could also potentially provide wider protection against certain mutations or variants of the SARS-CoV-2 virus.
  • Can cover up the shortages of Vaccines: Current Covid-19 vaccine production cannot sufficiently cater to the existing demand, resulting in stock-outs. Hence, in the short term, mixing solves the shortage of vaccines problem.
  • Safety Concerns: Countries like Germany, UK have halted the use of the AstraZeneca vaccine in younger age groups due to concerns of rare blood clots. Here, mixing and matching will allow the completion of immunization while ensuring safety.

Also Read: India needs an effective vaccine policy


  • Many unknowns: The Covid-19 vaccines in use have received restricted emergency use permissions. Hence, questions about how safe it is to mix and match and whether the approach can prompt a better immune response are still being answered.
  • Untested Combinations: Some vaccines like Covaxin have not even been administered in a mix and match scenario. Hence, more research needs to be conducted.
  • Differences in Vaccines: There are complexities in mixing vaccines which includes
    • differences in the shelf life of these vaccines
    • shipment and storage conditions
    • Some vaccines may have more side effects or may not work.
  • Side effects: Studies such as the Com-COV trials have shown that some combinations like AstraZeneca with Pfizer vaccines could lead to an increase in side effects.

Source: Indian Express


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