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

The government said it based its decision on the COVID Working Group, chaired by Dr NK Arora that reviewed the available real-life evidence before recommending the extension of the gap between the two doses.

May 14, 2021 / 08:28 AM IST
A vial of the Oxford University-AstraZeneca COVID-19 vaccine, which is produced in India and marketed as Covishield (Image: Reuters/Gleb Garanich)

A vial of the Oxford University-AstraZeneca COVID-19 vaccine, which is produced in India and marketed as Covishield (Image: Reuters/Gleb Garanich)

The government on May 13 decided to extend the present gap between the two doses of Covishield vaccine from 6-8 weeks to 12-16 weeks.

Serum Institute of India (SII) manufactures and distributes the Oxford University-AstraZeneca vaccine under brand name Covishield.

However, no change in interval of Covaxin doses was recommended. For Covaxin, the gap between two doses remains 28-42 days.

Here is an explainer on what made the government change its mind on dosing gap, what evidence did it based upon and did limited supplies of vaccine weigh on the government for this decision.

What evidence did the government based upon for this extension?

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COVID-19 Vaccine

Frequently Asked Questions

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How does a vaccine work?

A vaccine works by mimicking a natural infection. A vaccine not only induces immune response to protect people from any future COVID-19 infection, but also helps quickly build herd immunity to put an end to the pandemic. Herd immunity occurs when a sufficient percentage of a population becomes immune to a disease, making the spread of disease from person to person unlikely. The good news is that SARS-CoV-2 virus has been fairly stable, which increases the viability of a vaccine.

How many types of vaccines are there?

There are broadly four types of vaccine — one, a vaccine based on the whole virus (this could be either inactivated, or an attenuated [weakened] virus vaccine); two, a non-replicating viral vector vaccine that uses a benign virus as vector that carries the antigen of SARS-CoV; three, nucleic-acid vaccines that have genetic material like DNA and RNA of antigens like spike protein given to a person, helping human cells decode genetic material and produce the vaccine; and four, protein subunit vaccine wherein the recombinant proteins of SARS-COV-2 along with an adjuvant (booster) is given as a vaccine.

What does it take to develop a vaccine of this kind?

Vaccine development is a long, complex process. Unlike drugs that are given to people with a diseased, vaccines are given to healthy people and also vulnerable sections such as children, pregnant women and the elderly. So rigorous tests are compulsory. History says that the fastest time it took to develop a vaccine is five years, but it usually takes double or sometimes triple that time.

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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.
Viswanath Pilla is a business journalist with 14 years of reporting experience. Based in Mumbai, Pilla covers pharma, healthcare and infrastructure sectors for Moneycontrol.
first published: May 13, 2021 09:23 pm

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