As India's COVID-19 vaccination drive moves ahead, the Union government has decided to study whether the Covishield vaccine can be administered as a single dose instead of two shots.

Covishield vaccine has been developed jointly by the United Kingdom's Oxford University and British-Swedish pharmaceutical firm AstraZeneca. It is being manufactured in India by the Serum Institute of India. It is known by the name Covishield in India and as Vaxzevria outside. Recently, the government had increased the gap between two doses of the Covishield vaccine from 4-6 weeks to 12-16 weeks.

As per media reports, if the government takes a decision on administering Covishield in a single-dose regimen, it would help cover a much wider base of the population quickly. Reports suggest that the Covishield vaccine was initially planned as a single-shot jab but it was finalised as a two-dose vaccine following studies on its effectiveness. According to media reports, there is a view in the government that Covishield should also work as a single-dose vaccine as other jabs based on a similar platform like the Sputnik V Light and Johnson & Johnson's Janssen vaccines are also administered in a single dose.

A Public Health England study found that two doses of the Pfizer/BioNTech or the Astra/Zeneca vaccine protect against the COVID-19 variant first detected in India as well as the variant first found in the United Kingdom.

Two doses of the AstraZeneca vaccine is 60% effective against the B.1.617.2 variant and 66% effective against B.1.1.7, the study said.
But one dose didn’t work nearly as well. Three weeks after the first dose, the vaccine provides only 33% effectiveness against B.1.617.2 and 50% effectiveness against B.1.1.7. Thus, various experts believe one doze is not enough and requires a booster dose as well.