Results from a large study, which includes the Indian Council of Medical Research (ICMR), indicate that both Covishield and Covaxin significantly reduce the risk of severe Covid-19 and against the Delta variant among Indians aged 45 years and above. The study, pending peer review, was published on a preprint recently.
The overall effectiveness against severe Covid was 80 per cent with two doses of Covishield, and 69 per cent with two doses of Covaxin.
Vaccine effectiveness was highest with a 6-8 week interval between two doses of both vaccines. However, according to senior author Dr Manoj Murhekar, Director of ICMR–NIE (National Institute of Epidemiology), there were not enough numbers to gauge a 12-week interval. “The main point here is vaccines are effective. We do not really need a booster immediately as by June this year at least 60 per cent of the country’s population was infected with SARS-CoV2 and vaccination would have served as a boost to the immune system,” he said.
Another senior author, Dr Pragya Yadav, from ICMR-National Institute of Virology, said Covaxin and Covishield were effective against severe Covid-19 during the dominance of Delta variant in the second wave.
Main author Tarun Bhatnagar from ICMR-NIE, Chennai, said an escalation of the two-dose coverage with vaccines is critical to control the pandemic in the country.
The study was conducted between May and July 2021 in 11 hospitals. Of 1,073 cases of severe Covid and 2,264 controls (Covid-negative individuals), 6 per cent cases and 17 per cent controls reported full vaccination, and 16 per cent cases and 28 per cent controls reported partial vaccination with Covishield. The effectiveness of full vaccination was 80 per cent.
Of 887 cases and 1,384 controls, 3.4 per cent cases and 5.3 per cent controls reported full vaccination and 16 per cent cases and 28.3 per cent controls reported partial vaccination with Covaxin. The effectiveness of full vaccination was 69 per cent.
The study was conducted along with researchers from Amrita Institute of Medical Sciences, Kochi; Hamdard Institute of Medical Sciences and Research, New Delhi; AIIMS-Jodhpur, JSS Medical College, Mysuru; Government Medical College, Nagpur; SRM Medical College, Chennai; JIPMER-Puducherry; Surat Municipal Institute of Medical Education and Research, AIIMS-New Delhi, Rishikesh, and Bhubaneswar; and ICMR-National Institute of Virology, Pune.
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