The Subject Expert Committee (SEC) of the Central Drugs Standard Control Organisation (CDSCO) has recommended mixing vaccine doses.
The SEC is in favour of mixing and matching Covishield and Covaxin vaccine doses and has recommended that permission be granted to Christian Medical College (CMC), Vellore, for conducting a clinical trial on mixing of Covaxin and Covishield.
Experts favour mixing
AstraZeneca vaccines or Covishield, in the case of India, are examples of adenovirus vaccines. Covaxin, on the other hand, is created using inactivated or a dead virus.
These vaccines are completely different and “work in a different way, they are manufactured in a different way, the way they initiate an immune response is also different,” Dr Rohan Sequeira, Consultant General Medicine, Jaslok Hospital and Research Centre, told Firstpost.
Dr Kate O’Brien, director of the World Health Organisation’s (WHO) vaccine unit told The Associated Press, “Based on the basic principles of how vaccines work, we do think that the mix-and-match regimens are going to work.”
Studies on mixing
In order to understand the safety and efficacy of mixing vaccines, various studies are being undertaken and are in different stages of completion. Since we know that these vaccines are safe for people and are effective against SARS-CoV-2, researchers have taken the next step to find out if they play well with each other and invoke a stronger immune response.
Spanish CombivacS trial consists of more than 600 people, who had received one dose of the AstraZeneca vaccine. Two-thirds of the participants were given Pfizer as their second dose. Preliminary results showed they developed 37 times more SARS-CoV-2 neutralising antibodies and four times more SARS-CoV-2-specific immune cells than those who got only one AstraZeneca dose.
Mixing vaccines is not a new technique. The first combined vaccine was created and administered in 1948 to treat individual diphtheria, tetanus, and pertussis (DTP) and was initially used to vaccinate babies and children in 1948.
People in India have received both vaccines
Atleast 20 people from Uttar Pradesh’s Siddharthnagar were given two different vaccines as their first and second dose. Their first dose was Covishield, whereas six weeks later, they were given a shot of Covaxin as their second dose.
So far, none of them have reported any side effects.
Other countries allow mixing
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.
China in April said it was formally considering mixing Covid-19 vaccine doses for jabs developed with different technologies.
The US has allowed mixing of Pfizer and Moderna vaccines asking the recipients to take the two shots with a gap of 28 days.
Response to Delta variant
The testing of mix and match Indian vaccines on the Delta variant is yet to be conducted. However, mixing and matching vaccines of different technologies — for example, a viral vector vaccine followed up with an mRNA vaccine like Pfizer’s — might encourage our immune system to build a wider response.
“They’re all ultimately looking at the same target protein here —the spike protein — but presenting that to the immune system in different ways is potentially a great way of actually generating a better and broader immune response,” the Oxford Group’s Professor Matthew Snape explained during an episode of The Economist Radio’s podcast, The Jab, on May 31. Professor Snape is the chief investigator in the group’s Com-COV trials to mix and match Covid-19 vaccines.
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