Doses of the same Vaccine or Mixing different Vaccines – Which provides better immunity against Covid-19?

Doses of the same Vaccine or Mixing different Vaccines - Which provides better immunity against Covid-19?

Amidst warnings of the Third wave of Covid-19 Pandemic, most citizens are desperately looking for vaccines. One of the ideas that are gaining momentum is that of mixing two vaccines for better protection. So far the ones that have been inoculated have been given two doses of the same vaccine. So is it a good idea to mix two different vaccines? DNI takes a look.

In May 2021 18 people from Uttar Pradesh were accidentally given Covaxin second dose even though they had received Covishield first dose. The study compared the results of 40 people who were provided with both doses of Covishield and Covaxin against the results of the 18 people who received two different doses of Covishield and Covaxin. Here is what the study reported – “Overall, this study demonstrates that immunization 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”.

What is the difference between Covishield and Covaxin?
Covaxin uses a whole virus where a disease-carrying virus or bacterium is taken first. The virus is rendered inactive by killing it using chemicals, radiation, heat, or other means. This requires careful lab conditions to grow, cultivate, culture and finally, this leads to long production time and also needs to be administered in multiple doses.

Covishield on the other hand is a Viral vector vaccine where proteins of a safe virus are used to trigger an immunogenic response without actually causing the disease. For doing this, the instructions for making particular parts of the pathogen of interest are inserted into the safe virus. The Safe virus thus acts as a platform/vector and delivers the protein to the body which in turn triggers an immune response in the vaccinated person.

So can Covaxin and Covishield be mixed for better results?
According to leading immunologist, Dr. Vineeta Bal Covishield will trigger only an anti-spike protein response since it is a Viral vector or platform that is responsible for transmitting protein that induces immunity in the vaccinated person. In conjunction with this Covaxin may be used as a booster second dose which is expected to boost anti-spike response to improve the fight against the SARS-CoV-2 proteins which are primarily used in making the Covaxin.
Vaccine cocktails may not be inferior and might be better than two doses of the same vaccine. However, this needs to be done with caution since while theoretically its merit can be argued there is little hard evidence in the form of clinical trial data to provide a green single for taking two doses of different vaccines.
Hence no matter how beneficial Vaccine mixing or cocktails can be there needs to be urgent Phase 3 clinical trials to prove the point. Till then it is better to stick to getting vaccinated with the same dose of the vaccine rather than mixing the doses. To quote Dr Sanjay Pujari who is an infectious diseases specialist and expert member with the national Covid 19 task force “The published evidence for efficacy and safety of heterologous vaccine strategies is limited to 2-3 phase 2 and cohort studies up to 1000 individuals… No large phase 3 trials assessing vaccine efficacy on the symptomatic illness of heterologous versus homologous strategies have been reported. These need to be urgently conducted”

Arunava Bhattacharya, DNI


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