Experts’ View On Mixing Covid-19 Vaccines

Experts’ View On Mixing Covid-19 Vaccines


A new surge of COVID-19 infections is being reported across countries. Partly to blame is the Delta variant, a mutated COVID-19 virus that is more easily transmissible and more resistant to vaccines. The other significant factor has been lagging vaccination rates, especially across poorer nations of the world which have been struggling to receive enough vaccine doses. As nations are getting by with whatever they have, and WHO is imploring wealthier nations to share vaccines, an unlikely solution may be to mix and match vaccines.

Here is all you need to know about mixing COVID-19 vaccines

The use of two different vaccines for inoculation is known as heterologous vaccination. Scientists acknowledge using a different manufacturer or vaccine for the second dose can boost the immune system in the body against the virus. To cite an example, AstraZeneca’s Covishield uses a modified and weakened chimpanzee ‘adenovirus’ (common cold virus) to deliver the genetic code of the SARS-CoV-2 spike protein to the body. By the second or the third dose the vaccine gets less effective.

The first dose of a vaccine in the body develops antibodies against the spike protein of SARS CoV-2 while the second dose develops antibodies against the adenovirus. When the 2nd dose of the same platform is injected, it can result in building a weaker immunity system.

This is the reason why Sputnik V has two different adenoviruses to deliver the spike protein’s code to bodies, says Dr Srinath Reddy, President, Public Health Foundation of India.

Dr Soumya Swaminathan, World Health Organization (WHO) Chief Scientist, said heterologous vaccination could work well, especially in countries facing vaccine shortages.

“It seems to be working well, this concept of heterologous prime-boost,” she said.

Paul Offit, Director, Vaccine Education Center, Children’s Hospital of Philadelphia, also concurs with Soumya Swaminathan’s views saying that inoculating using a combination is likely to offer longer immunity or fewer side effects for certain individuals.

Recent studies from Spain, testing the combination of the AstraZeneca and Pfizer vaccine showed effective preliminary results reported The Lancet.  “In conclusion, heterologous vaccination regimens against COVID-19 provide an opportunity to speed up vaccination campaigns worldwide, maximising their impact on the control of the pandemic,” stated the report from the famed medical journal.

Mixing and matching vaccines can also build a wider immune response for the body, thus, fighting against mutations and variants. In The Economist Radio’s podcast, The Jab, Oxford Group’s Professor Matthew Snape explained saying, the immune system gets a better and broader immune response if there is a mix and match.

Dr Reddy believes AstraZeneca’s Covishield is less effective against the Delta variant as has been seen in the UK. In India, it would make sense for the second dose to be different so the person is protected.

Chair of National Expert Group on Vaccine Administration for COVID-19 (NEGVAC) Dr V.K. Paul said, “It is plausible. But there needs (sic) to be more studies… One shot of one type produces antibodies and the second shot from another will increase that. Scientifically, there is no problem.”

The gap between the current production of COVID-19 vaccines against the numbers needed is huge, not only in India but across the world. Various state governments have had to stop vaccinations between the age group of 18 and 44 intermittently and the Union government had to stop manufacturers from exporting and fulfilling their obligations.

As India prepares to get 8 different COVID-19 vaccines by the end of the year, including vaccines using different biological platforms, a heterologous vaccination policy can ease a lot of the COVID-19 vaccine shortages.

India is already planning to run trials with all 8 vaccines, 3 of which are currently available and 5 which are currently in the pipeline.

What other countries are doing 

Many European countries, and Canada too, have stopped the AstraZeneca vaccine in younger age groups due to reports of rare blood clots. In this scenario, a mix and match of vaccines can help to build their immunity levels.

The Coalition for Epidemic Preparedness Innovations, looking into mixing and matching COVID-19 vaccines, has raised some questions about a possible heterologous inoculation policy — shelf life of the different vaccines, shipment and storage issues, side effects and effect on people with comorbidities. The recent COM-COV trials have proven that the AstraZeneca vaccine mixed with Pfizer vaccines lead to an increase in side effects, while showing improved effectiveness as well.

In spite of these challenges, countries are exploring the possibilities. Canada, UK and the EU are offering Pfizer or Moderna instead of AstraZeneca. South Korea and Spain are also looking at a mix and match. Not far behind are Russia and China, with Russia testing a combination of AstraZeneca and Sputnik V.

Malaysia is also exploring using combinations of AstraZeneca and Pfizer-BioNTech shots as they are lagging behind in the vaccination drive.

First Published:  IST


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