A two-dose regimen of the ChAdOx1 (Oxford-AstraZeneca vaccine) and Covishield vaccine did not show protection against mild-to-moderate Covid-19 due to the B.1.351 variant, according to a study published in The New England Journal of Medicine.
The findings came from a multicentre, double-blind, randomised, and controlled trial which involved HIV-negative adults who were assigned in a 1:1 ratio to receive two doses of vaccine or placebo, 21 to 35 days apart, between 24 June and 9 November 2020. Of the 750 vaccine recipients, 19 (2.5%) developed mild-to-moderate Covid-19 more than 14 days after the second dose compared to 23 (3.2%) of 717 placebo recipients. Vaccine efficacy is 21.9% (95% CI, −49.9 to 59.8). There were no cases of severe disease or hospitalisation. Among the 42 participants with mild-to-moderate Covid-19, 39 cases (92.9%) were caused by the B.1.351 variant (South African). Further, serum samples were obtained from 25 participants after the second dose was tested by pseudovirus and live-virus neutralisation assays against the original D614G virus and the B.1.351 variant. Both the pseudovirus and the live-virus neutralisation assays showed greater resistance to the B.1.351 variant in serum samples obtained from vaccine recipients than in samples from placebo recipients.
It is a very small study to comment on the effectiveness of this vaccine to prevent serious disease, hospitalisations, and death. If it remains effective in this regard, then it will still be very useful. This, after all, is why we developed vaccines against SARS-CoV-2. Oxford-AstraZeneca should expedite the efforts to develop second-generation Covid-19 vaccines targeted against B.1.351 and P1-like variants. The Government of India should open up the market for all available vaccines.
The writer is an intensivist at Sir Ganga Ram Hospital and a member of the IAP Pediatric Infectious Disease Chapter.