Explained: Will extending gap between two Covishield doses help save more people?

What evidence did the government based upon for this extension?

The government said it based its decision on the COVID Working Group, chaired by Dr NK Arora that reviewed the available real-life evidence, particularly from the UK, before recommending the extension of the gap between the two doses. The AZD1222 vaccine against COVID-19 has an efficacy of 63.09 percent against symptomatic SARS-CoV-2 infection. Longer dose intervals within the 8 to 12 weeks range are associated with greater vaccine efficacy.

According to a study published in the medical journal the Lancet on March 6, the efficacy of the AstraZeneca vaccine rose from an average of 55.1 percent (when two standard doses are administered at a gap of fewer than six weeks) to 81.3 percent when the interval is at least 12 weeks. The data was based on 17,178 participants in trials from the UK, Brazil, and South Africa.

Why did it take so much time for Indian government to extend the dosing interval?

The bridging clinical trial of Covishield in India is based on four week or 28 days dosing intervals. The Covishield’s bridging studies in India did not include dosage variables. Even WHO panel supported the 12-week interval, based on the higher immunogenicity and efficacy benefits that came with a longer gap.

How beneficial is it to expand dosing gap?

The UK government, when it was faced with a surge in cases in December and January due to a new variant called B.1.1.7, decided to maintain a long gap of up to 12 weeks between doses of the Oxford-AstraZeneca vaccine. The rationale behind this is that giving more people the first dose right away will lead to fewer deaths and less pressure on the country’s already overwhelmed healthcare services. Indian policy makers are currently grappling with a similar situation where there are limited supplies of COVID-19 vaccine, and about 4,000 people are dying daily.

The aim is to protect as many people as possible from COVID-19. Experts such as Dr Gagandeep Kang, who is also a member of the COVID Working Group, told Moneycontrol early this week that maybe "all adenovirus vaccines are inducing maximal effect with the first dose" at least for short term protection. Covishield is based on the Chimpanzee adenovirus vector.

Breathing space for SII

The decision is not a breather for the government, but also for the SII, which is struggling to expand capacities to meet the growing demand. With no other COVID-19 vaccine expected in a big way in next 2-3 months, SII with about 90 percent share in the total COVID-19 vaccination, and with further extension of gap between doses, will continue its dominance. About 90 percent of the 17.7 crore doses administered in India are Covishield. At the moment, combining two different doses of vaccine is not allowed.