Studies point to better protection with mixed doses; experts call data ‘fragmentary’
India started administering COVID-19 vaccine booster dose January 10, 2022, for healthcare workers and those aged more than 60 with comorbidities. VK Paul, head of India’s COVID-19 task force, had said no mixing of doses will take place for boosters.
Those who received two doses of Covishield (manufactured by Serum Institute of India) will receive the same vaccine as the third dose. The same goes for Covaxin (manufactured by Bharat Biotech International Ltd) and Sputnik.
But do we really know what the best option is?
India has been administering Covishield — 90 per cent of the population has received this vaccine — Covaxin and Sputnik V in the last one year. While Zydus Cadila’s ZyCoV-D has been authorised for use, it has not been administered so far.
Indian authorities recently also cleared Hyderabad-based Biological E’s Corbevax and Serum Institute of India’s Covovax — both of which are protein-based vaccines — for emergency use authorisation.
This gives India five vaccines to choose from when administering a booster dose. However, experts believe a dearth of data on not just the efficacy of mixing vaccines but also administering the third dose altogether cannot be ignored.
Evidence till now accounts for reduced antibodies, but several studies, yet to be peer-reviewed, argue that the immune system’s T cell response remains intact even against omicron. This means that two doses of a vaccine continue to protect us against severe disease.
Moreover, pre-prints put forth data that suggests booster dose provides increased protection against omicron and that mixing vaccines — such as two shots of AstraZeneca followed by one of Pfizer Inc — put up better protection than three doses of the same vaccine. It remains unclear for how long the magnitude of immune response increases.
“No clinical studies have been conducted in India on mixing vaccines so far. We can’t apply the data of the United Kingdom population to India. Unless a trial is conducted here, and it has positive results, we cannot and should not mix doses,”