India on Sunday approved two COVID-19 vaccines for emergency use - Covishield and Covaxin. While the Oxford-AstraZeneca vaccine that is being manufactured in India by the Serum Institute has shown an average effectiveness of 70%, Bharat Biotech's Covaxin is a few steps behind - with third phase trial data yet to be made public.
The Oxford vaccine had shown 90% efficacy in one dosing regimen when the vaccine was given as a half dose, followed by a full dose at least a month later, and another dosing regimen showed 62% efficacy when given as two full doses at least one month apart. The average was somewhere around 70%. However, corresponding data is not yet available for Covaxin and third phase trials are presently underway. Previous estimates made by Bharat Biotech's had said that their vaccine offering was expected to be 60% effective. Both the vaccines have to to be administered in two doses and must be stored at 2-8° C.
While the effectiveness of the two vaccines are comparatively lower than other approved vaccines it is well above the percentage required by India’s top drug regulator which requires vaccine candidates to show the desired response in at least 50% of those vaccinated during human testing.
The fact that trials for Covaxin continue to be underway has created a furore with many opposition leaders striking a cautionary note. However, Union Health Minister Dr Harsh Vardhan clarified on Sunday night that the permissions given to the two vaccines are slightly different.
As he put it, Covaxin was intended to act as a backup vaccine of sorts at present, as trials were completed. "For those spreading rumours let it be known that emergency use authorisation for COVAXIN is differently conditional – in clinical trial mode. All COVAXIN recipients to be tracked, monitored as if they’re in trial. COVAXIN approval is ‘Monitored Approval’ with strict follow-up and rolling review," he explained.
The two vaccines are also not identical. While two dose vaccines, the gap between the two shots is likely to be different for the two vaccines. Pune-based SII's shot is a Recombinant Chimpanzee Adenovirus vector vaccine, encoding the SARS-CoV-2 Spike (S) glycoprotein with technology transfer from AstraZeneca/Oxford University.
Covaxin on the other hand is a a Whole Virion Inactivated Coronavirus Vaccine that was developed in collaboration with ICMR and NIV (Pune), from where they received the virus seed strains. The vaccine was developed on the Vero cell platform.
(With inputs from agencies)