Earlier this week, around 20 villagers in Uttar Pradesh’s Siddharthnagar district had been given a dose of the Covishield vaccine and received Covaxin for the second dose at a government hospital – a mistake that local officials have attributed to administrative oversight. This incident raised many questions on what happens if we mix the doses of vaccines?
In India, the question of efficacy and more importantly the safety of mixing and matching vaccinations has become more pertinent now in the face of vaccine rollout delays thus slowing down the innoculation drive with partially vaccinated people left hanging for their second doses.
Moreover, new waves of Covid-19 and the threat of new variants breaching the vaccine’s protection have led to the possible need for a third booster dose being looked at.
However, in the absence of evidence and regulatory approvals, both of which are completely lacking, I will suggest that mixing of vaccines be done only on the basis of scientific data and clinical trials, said Dr. Wasim Ghori Mumbai based Consultant Physician & Diabetologist and Fellow – Royal Society of Public Health, UK.
Meanwhile, Dr. Ghori said, it is important to note that some countries have already allowed mixing vaccines in emergencies with early trial results suggesting some combinations are safe and potentially more effective. All approved vaccines need two doses. Generally, the first dose primes the immune system to recognise the virus, and the second boosts the recognition and response to it.
Combining vaccines, say with the first dose of a viral vector vaccine-like Oxford-AstraZeneca’s Covishield and a second dose of an mRNA jab like Pfizer-BioNTech, is called Heterologous Prime-Boost and it could train the immune system to recognise the virus in more than one way, he added.
Russia’s Sputnik V is a ‘Combination Vaccine’ by design. The first dose uses a harmless Common Cold Adenovirus (Ad26) to deliver genetic instructions for cells to produce the coronavirus’s spike proteins. The second does it with a different Adenovirus (Ad5) to avoid being attacked by the immune system that now recognises Ad26.
The mechanism works as Sputnik V has an efficacy rate of 91.6% similar to Pfizer and Moderna’s mRNA vaccines, although it is a viral vector shot like Covishield.
Given the above, there isn’t enough data yet in India to recommend this type of combination. Hence, vaccines should not be mixed without proper clinical trials.
Dr. Amit kumar Shah, DNB Medicine, Consultant Physician at AXIS Hospital explained, “In India, currently there is no research data available for mixing Covishield with Covaxin in their differwnt doses. As far as we know, mixing vaccine isn’t completely unsafe and may be plausible in the near future, but it might just intensify the side effects like fatigue, chills, fever, headache, etc.”
As there are no active trials in India, more concrete results from international studies in few months may make mixing vaccines in India common. However, more studies are needed for this to be safe advice, said Dr. Shah.
He added, there have been trials conducted in the UK that tested mixing and matching Pfiezer and AstraZeneca (Covishield) in 600 participants. The study reported that if the Pfizer vaccine was given as a second dose after the first dose of Covishield, the immune response against the SARS-CoV-2 virus was potent.
However, safety data from a similar mix-and-match study also revealed that participants reported higher side effects. Canada, Finland, France, Norway, Sweden, Spain, and South Korea have allowed the use of a different vaccine for the second dose for complete Covid-19 vaccination if the first dose was of AstraZeneca vaccine. The US has also allowed Moderna and Pfizer to be paired.
Right now, in India however, the protocol of giving the same vaccine for both doses must be followed.
On the other hand, according to Dr. Umesh Khanna, MD, DNB Director, Kidney Associate, trials are being conducted to study the effect of mixing of vaccines in India. However Spanish trials have shown good results. In a country like India where we are facing shortage of vaccines, mixing of vaccines if found successful, will be a great boon to our vaccine programme.