A mistake that should be avoided, or a solution that has the potential to be a game-changer in the Covid-19 fight, what is the truth about mixing two separate vaccines? There has been a hue and cry after health officials in UP said that a group of people were accidentally given a dose of Covishield followed by one of Covaxin. But the Centre has sought to soothe fears of adverse reactions in such cases. Experts worldwide have studied the scope of combining vaccines to see if that gives greater protection against infection, but the fact remains that unless you are in a trial, or there is an official nod to mixing vaccines, you should not go for combining separate doses for your two shots.
ISN’T IT UNSAFE TO TAKE TWO SEPARATE VACCINES?
The general consensus among experts is, no, there is theoretically no danger in mixing vaccine shots. But whether or not two separate vaccines can be mixed should only be determined after careful scientific study and trial. Lending clarity to the matter, Dr VK Paul, the Chair of NEGVAC (National Expert Group on Vaccine Administration for Covid-19), had said last week, “It is plausible. But there need 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.”
But he stressed on the need for rigorous research to establish that two vaccines can indeed be mixed. “It can’t be said definitively that mixing of doses can be practised. There is no robust scientific evidence. Only time will tell whether it will be done in future or not, It will depend on international studies, World Health Organisation (WHO) findings, etc. Our experts are also continuously studying,” Paul had further explained.
After the ‘mix-up’ came to light in UP’s Siddharthnagar district earlier this week, Paul reiterated that “even if two doses of two different vaccines are given, this should not be a cause of concern”. He reiterated that “more scrutiny” is needed, but added that “any significant adverse effect is unlikely”.
WHAT HAVE STUDIES SAID ABOUT COMBINING VACCINE DOSES?
The chance of combining two separate vaccine doses holds its attractions at a time when governments across the world are struggling to resolve supply-chain bottlenecks to keep their vaccination drives running smoothly . For countries that have given emergency nods to multiple vaccines, it will give them the flexibility to continue inoculating their populations in a situation where one
vaccine runs out but another is available.
Which is the reason why trials are on around the world that are combining doses to see what impact mixing vaccines has on their efficacy in boosting the immune response, and whether there are any serious adverse effects that may crop up due to such a strategy.
One such trial, ongoing in the UK, that combined the Oxford-AstraZeneca shot with the one produced by Pfizer-BioNTech, found that the pairing seems to up the likelihood of mild to moderate side effects although no serious adverse outcomes were seen, the journal Lancet reported. The trial is studying four combinations of these two vaccines, two in which both shots are of the same vaccine while the other two have the two vaccines combined, but with their orders alternated: Oxford/AstraZeneca (which is being used in India under the name Covishield) + Pfizer/BioNTech, and Pfizer/BioNTech + Oxford/AstraZeneca.
On the whole, the two mixed doses were reported to have caused more side-effects. Feverishness was flagged by 34% of patients who got Oxford/AstraZeneca followed by Pfizer/BioNTech and 41% of those given Pfizer/BioNTech followed by Oxford/AstraZeneca. But only 10% of those who got two shots of the Oxford-AstraZeneca jab reported a similar symptom while the figure was 21% for those who received two Pfizer/BioNTech doses.
Though the adverse events were “short-lived and there were no other safety concerns”, similar observations were noted for chills, fatigue, headache, joint pain, malaise, and muscle ache following vaccination with two separate doses. However, the data on how effective the various combinations were in boosting immunity is still awaited.
One hint in though came from a study in Spain, which found that mixing the Oxford–AstraZeneca shot with the Pfizer–BioNTech one “produces a potent immune response against the virus”.
As part of this study, people who had received a first dose of the Oxford-AstraZeneca vaccine were given the Pfizer-BioNTech shot after a gap of at least eight weeks. The participants who got the mixed dose were found to have produced much higher levels of antibodies than they had after the first shot.
IS ANY COUNTRY ALREADY GIVING MIXED DOSES?
As would be evident by now, mixing vaccines is not just a matter of putting the first two available into any recipient’s arm but of carefully studying adverse reactions and also the ultimate gains in immune response that such a combination imparts. Experts have pointed out that since the goal of all vaccines that have been cleared for use so far is to train the body’s immune system to recognise and attack the novel coronavirus‘ spike protein, which it uses to invade human cells, differences in the type of vaccine used can only matter so much.
In fact, exploring the scope for combining vaccines is also significant given that adverse events reported with some jabs, including with the Oxford-Zeneca one, can contribute to an unwillingness among people who received it for their first dose to show up for the second one.
Health officials in several countries have by now recommended mixing of doses. For example, Finland’s Institute of Health and Welfare has said that people under 65 who received a first dose of the Oxford-AstraZeneca vaccine may get a different shot for their second dose while France’s top health advisory body has said that people under 55 who got a first shot of the Oxford-AstraZeneca vaccine should receive a second dose of an mRNA vaccine, like the Pfizer or Moderna one, although the country has not done a trial for mixing the doses.
However, the UK has said that only in rare cases would it allow people to be given a different vaccine for a second dose, for example if the first vaccine was out of stock. As for the US, its public health watchdog is reported to have given the nod, only for “exceptional situations”, to mix the Pfizer-BioNTech and Moderna vaccines at a gap of at least 28 days.
In India, no trials have been held yet on combining the Covishield and Covaxin vaccines that are the two primary shots in the country’s vaccination drive. So, to go back to what experts here have said, it is open to trials to suggest how effective and safe it would be to mix vaccines. As has been stressed, without this data and a green light from health authorities, two different vaccines should not be combined.
