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Explained: should gap between Covid-19 doses be increased?

Apr 13, 2021 11:58 IST | By Editorji News Desk

As India reels under the second wave of coronavirus, there have been calls from several quarters to open vaccination to everyone by removing the age bar. But the proposal has also set off alarms about inadequate supply of vaccines. This in turn has led to suggestions that the gap between two doses of a vaccine should be increased so that maximum population can be inoculated with the life-saving jab.

Is the suggestion feasible? Will it reduce the efficacy of the vaccine? Will it help help solve the demand-supply equation?

Before we get to those answers, first let’s see how 2-shot vaccines work.

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The job of the first jab is to build immunity, generate the necessary anti-bodies, the job of the second is to ramp up the process and re-inforce the immunity. The body doesn’t immediately generate immune response after getting the first dose, it’s a slow process and usually takes around 3 weeks.

Dr Gangandeep Kang told Indian Express that it can take up to eight weeks or longer for the antibodies to become fully functional and said that gap between two doses should not be less than 3-4 weeks.

Experts say that the risk with giving the second dose too early is that it doesn’t give the immune system enough time to react to the first dose so that it can maximise benefits of the second dose.

However, the required interval between the two doses differs from vaccine. Results of Oxford Vaccine Trials reviewed by The Lancet say that a single dose of the Oxford-AstraZeneca vaccine showed 76% efficacy from day 22 to day 90, which means that efficacy of the drug had not reduced between. The report also suggested 3 months or 12 weeks as an effective gap. Vaccine-maker Pfizer on the other hand has recommended that the gap between jabs of their drug be 3 weeks, and that it should be given after 6 weeks only in special situations.

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In India, while Covishield doses are administered in a gap of 6-8 weeks, the cut-off for Covaxin is 4 weeks. In fact, the interval for Covishield earlier was 4-6 weeks but the govt extended it to 4-8 weeks while saying that the protection offered by the drug is enhanced if given between 6-8 weeks. Though it did add that the gap should not be longer than 8 weeks.

Vaccine expert Dr Gangandeep Kang has told India Express that it is worthwhile to increase the interval if it gives a greater degree of protection and provides good immunity with a single dose. This also solves the problem supply constraints, he added. It gives more time for production of more vaccines.

Though he advised against it if one dose of a 2-shot vaccins does not generate good or required amount of immunity.

Countries like UK, Germany, France and Canada have already increased the gap between 2 doses to accelerate the inoculation drive, ensure maximum efficacy and also to deal with shortage of supplies.

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France is set to extend the period for mRNA vaccines to 6 weeks from 4 weeks starting April 14. In Germany, the time period has been increased to 12 weeks for the Oxford drug. In UK, the gap was stipulated at 10-12 weeks for all vaccines but the experts called upon them to reduce it for Pfizer. Canada administers it Covid-19 vaccine doses at a gap of 4 months.

Now, given that there is urgent need for maximising vaccination in India that is not helped by the reports of shortfall in vaccine, extending the time between 2 doses of Covishield, which has a recommended gap of 12 weeks, does seem to present itself as a good option. However, Covaxin unlike Covishield is an inactivated vaccine and Dr Kang says that such vaccines do better with shorter intervals.

Whether the Indian govt increase the interval between two jabs are not, the purpose of these vaccines is to decrease the severity of disease, prevent hospitalisation and reduce deaths due to Covid-19. They do not prevent you from contracting the disease all together.

So mask up, wash your hands and maintain appropriate social and physical distance.

Also Read | Know your vaccines: How do Sputnik V, Covaxin and Covishield work?