A single shot of the Covishield vaccine has an efficacy of 61% against the Delta variant of coronavirus, while two doses provide 65% protection, NK Arora, the head of India’s Covid-19 Working Group of the National Technical Advisory Group on Immunisation, told NDTV on Wednesday.

In an interview to the news channel, Arora referred to a study conducted by the Christian Medical College in Vellore, which was first reported last week. Arora said that the study was conducted “in the middle” of the second wave of the pandemic, which was majorly caused due to the B.1.617, or Delta variant, first detected in India.

The study, which is yet to be peer-reviewed, involves observations made on 8,991, or 84.8% of its staff members who received the Covishield vaccine, while the remaining were administered Covaxin. The study reports the incidence of symptomatic Covid-19 infection among the workers between February 21 and May 19.

Besides the vaccine efficacy quoted by Arora, the study also showed that one dose of the Covishield shot reduced the risk of hospitalisation by 70% and two doses by 77%.

In his interview, Arora said that the Covid Working Group and the National Technical Advisory Group on Immunisation relied on the data from studies conducted by the Vellore Hospital and Post Graduate Institute of Medical Education Research in Chandigarh, before extending the gap between two doses of the Covishield vaccine.

Data from the Chandigarh hospital showed 75% efficacy of Covishield against the Delta variant, Arora said. But he added that this study was conducted earlier and did not take into account the full impact of the second wave in India.

Arora’s comment on the gap between doses came amid a controversy after three scientists of the National Technical Advisory Group on Immunisation, or NTAGI, said that they did not back the Centre’s decision last month to double the interval between two doses of the Covishield shot. Arora denied their claim, suggesting that the decision was taken on a “scientific basis” and without any “dissenting voice”. On Wednesday, Union Health Minister Harsh Vardhan also said that the decision was taken in a “transparent manner” and was “based on scientific data”.

Arora also told NDTV that there was a “strong chance” that the world will ultimately depend on India for affordable and effective vaccines against Covid-19. “Ultimately the world will be dependent on us for vaccines,” he said, but added that his comment was “very premature, very presumptuous”.

The Covid Working Group chief based his assertion on the prospects of the Novavax vaccine, being developed by Covishield-maker Serum Institute of India and another shot being manufactured by Hyderabad-based Biological E.

“Novavax is very exciting,” Arora said. “In the past week it has created a rage because India is going to manufacture almost a billion doses a year. It is going to be simple and cheaper with a 90% vaccine effectiveness.”

As for the Biological E shot, Arora said that it was undergoing phase 3 trials and may be sold at an “incredibly low” price of Rs 250 for two doses.