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Increase Covishield dose gap to 6-8 weeks, Centre tells states

This time interval between two doses has been revised only for Covishield and not Covaxin.

March 23, 2021 / 12:05 AM IST

The interval between two doses of Covishield vaccine should be increased to six-eight weeks, the Centre has said in a letter to state governments on March 22. At present, the two-dose vaccine is being administered four to six weeks apart.

Based on the feedback received from the National Technical Advisory Group on Immunization (NTAGI) and subsequently by the National Expert Group on Vaccine Administration for COVID-19(NEGVAC), it was decided to recommend an increase in the interval period between the two Covishield doses, the government said in a statement.

"Keeping the existing scientific evidence in view, it appears that protection is enhanced if the second dose of Covishield is administered between six to eight weeks, but not later than stipulated period of eight weeks," the Centre said.

The decision has been conveyed to states and union territories through a letter written by Union Health Secretary Rajesh Bhushan.

"In view of the emerging scientific evidence, the interval between two doses of a specific COVID-19 vaccine ie Covishield, has been revisited by NTAGI and NEGVAC in its 20th meeting," the statement read. "This decision of revised time interval between two doses is applicable only to Covishield and not to Covaxin vaccine."

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COVID-19 Vaccine

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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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India has approved two vaccines for coronavirus. Oxford-AstraZeneca's Covishield is being manufactured at Pune's Serum Institute of India (SII). Covaxin has been developed by Hyderabad-based Bharat Biotech.

"The Union Health Secretary has urged the states and UTs to instruct the concerned officials accordingly to undertake necessary steps to widely disseminate the message of revised dosing interval among programme managers, vaccinators and recipients of Covishield vaccine," the government has said.

The decision to increase the interval period also comes in the backdrop of World Health Organisation's (WHO) recommendation to administer the two doses of AstraZeneca vaccine after a gap of eight to 12 weeks.

"In light of the observation that two-dose efficacy and immunogenicity increase with a longer interdose interval, WHO recommends an interval of 8 to 12 weeks between the doses. If the second dose is inadvertently administered less than 4 weeks after the first, the dose does not need to be repeated," the expert panel of the UN-linked body said.

Also, a recent study published in British medical journal Lancet said a 12-week or three-month interval before the second dose provides better protection.

The study said vaccine efficacy after the second dose was even higher at 81.3 percent in those with a dosing interval of 12 weeks or more versus 55.1 percent in those with an interval of less than six weeks.
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