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Sunday, April 18, 2021

Gap between Covishield vaccine doses increased: Everything you need to know

Even though the global studies said that efficacy increased if the interval of the doses were increased to 12 weeks, the main reason why India did not extend it beyond eight weeks is that the data is not very convincing. Here's all about why the government did increased the gap between doses

The Indian government wrote to all the chief secretaries of the states and administrative heads of the Union Territories of India and asked them to increase the interval between the two doses of the vaccine Covishield. As part of the nationwide inoculation drive, Covishield and Covaxin are the two vaccines that are being delivered at this point. Now, the question is why was the gap between Covishield vaccine doses increased? Here’s everything you need to know.

The notice was sent on Monday. But there was confusion if the government wanted to increase the interval of both the vaccines or just the AstraZeneca-Oxford University’s Covisheild. The Narendra Modi-led central government clarified on Tuesday that the notification was meant only for Covishield and not Covaxin.

Why did the government bring out this order?

The government order came after the National Technical Advisory Group on Immunization (NTAGI) and the National Expert Group on Vaccine Administration for COVID-19 (NEGVAC) made recommendations in their 20th meeting.

What has the government asked states and UTs to do?

“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 8 weeks,” the Health Ministry has said. Union Health Secretary Rajesh Bhushan, who had written the letter to the administrators of the states and the UTs, has also asked that the states and UTs instruct all officials concerned to take every step necessary to inform programme managers, those administering the vaccine and the people who come to get vaccinated of the Covishield vaccine of the revised dosing interval. Not only that, they were asked to ensure that the people adhere to the new directive of the revised dosing interval.

What did the experts say?

According to the letter sent to the state and UT administrators, the centre said that the NTAGI and NEGVAC reconsidered the currently applicable interval which was being followed throughout the country because there has been some new scientific evidence that has come to light. t showed the efficacy increased when the second dose was delivered six to eight weeks after the first dose was given to the recipient.

The vaccine Covishield is Serum Institute of India’s version of the vaccine which AstraZeneca had developed in collaboration with the University of Oxford — AZD1222. Some of the data from various trials across the globe have found out that if the duration between doses is increased to 12 weeks then the efficacy increased a lot. But on the other side of things, interim findings from trials in the US, Peru and Chile have shown that the vaccine had an efficacy of around 79 per cent even if the second dose of the vaccine was administered four weeks after the first dose was received.

Gap between Covishield vaccine doses increased, why so?

Even though the global studies said that efficacy increased if the interval of the doses were increased to 12 weeks, the main reason why India did not extend it beyond eight weeks is that the data is not very convincing and the experts’ group concluded that the vaccine’s efficacy would not increase if the duration is extended beyond eight weeks, said the letter from Health Secretary Bhushan.

The experts said that there was no good scientific evidence for them to recommend that the interval should be increased beyond eight weeks. The delaying is increased for countries that have a dearth of vaccines. Since India has been producing it, the country has enough vaccines and thus it does not make sense to increase the period of interval between the two doses.

But there might be potential risks. And that is the other reason why the interval was kept to eight weeks. If the first vaccine shot is delivered and a 12 week period is provided in between, it only increases the chance of the person spreading the infection to others. Even though the extended dosing interval means that more antibodies will be formed in the person’s body, it does not always mean that it will guarantee better protection — there is no direct correlation.

What about the latest findings?

Oxford University and AstraZeneca have said that interim results from the third phase of clinical trials which was conducted on 32,000 people across the United States of America, Chile and Peru have shown that the vaccine has an efficacy of 79 per cent against the symptomatic Coronavirus (COVID-19) if the interval between the doses administered was kept to four weeks. What is more important is that the effectiveness was 100 per cent in the cases where the virus was severe or was a critical symptomatic COVID-19 trait. These results show much higher efficacy than the results from the United Kingdom and Brazil.

What do other studies say about this vaccine’s dosing interval?

The data from various trials of the AZD1222 — or as we call it in India, Covishield — in other countries show that the effectiveness of this vaccine gets a boost when the second dose is administered more than six weeks after the first dose is given to the person. The effectiveness means how fast the vaccine can bring down cases of symptomatic COVID-19 in those vaccinated as compared with those people who have not been vaccinated.

A study that was submitted to Lancet but has not been peer-reviewed yet, says that the vaccine’s efficacy stood at 54.9 per cent if the second dose was administered very soon — less than six weeks interval. It increased to 59.9 per cent if the interval was anything between six to eight weeks. It increased further to 63.7 per cent if the second dose was after 9-11 weeks, and 82.4 per cent if the dosing interval extended to 12 weeks or more.

How will this change India’s vaccination campaign?

If the second dose is delayed it could mean that there will be more doses for a larger number of people available at any point, if the supply remains the same. This means that you can get your first vaccine shot sooner. It will also help the ones most vulnerable and the ones most exposed to get vaccinated faster.


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