4 min readMumbaiMar 23, 2021 03:52 AM IST
First published on: Mar 23, 2021 at 12:17 AM IST
The central government on Monday revised the time interval between two doses of Covishield, directing states to increase it to 4-8 weeks from the current protocol of 4-6 weeks.
The Union Ministry of Health and Family Welfare took the decision on the recommendation of two expert groups — the National Technical Advisory Group on Immunisation (NTAGI) and National Expert Group on Vaccine Administration for Covid-19 (NEGVAC).
“During this meeting the recommendation has been revised to provide 2nd dose of COVISHIELD at 4-8 weeks’ interval after the first dose, instead of earlier practised interval of 4-6 weeks. This decision of revised time interval between two doses is applicable ONLY to COVISHIELD and NOT to COVAXIN vaccine,” the Ministry said.
Union Health Secretary Rajesh Bhushan wrote to states that based on the scientific evidence, it “appears that protection is enhanced if the second dose of COVISHIELD is administered between 6-8 weeks, but not later than stipulated period of 8 weeks”.
Data on the Co-WIN dashboard show 4.22 crore doses of Covishield have been administered so far during the country’s vaccination drive. Of the total 4,61,07,627 doses administered, including both Covishield and Covaxin, the second dose has been given to only 74,84,953 beneficiaries so far. After Monday’s announcement, the schedule for the second dose will change for all Covishield recipients in this group.
India’s decision comes in the backdrop of global trials that have shown that an extended interval of up to 12 weeks demonstrated greater efficacy in the Oxford-AstraZeneca vaccine, of which Covishield is a version. The trials have also suggested that administering the second dose with an interval longer than four weeks could further increase efficacy. Importantly, delaying the second dose allows a larger number of people to get their first shots of the vaccine sooner.
ExplainedGreater vaccine efficacy
India’s decision on the second dose for Covishield comes after the WHO’s expert team recommended that a longer interval between 8 and 12 weeks between the two doses are associated with greater vaccine efficacy. Britain was the first country to extend the interval between the initial and booster doses of the AstraZeneca vaccine to 12 weeks.
On Monday, AstraZeneca announced the results of phase 3 trials of the vaccine in the United States, which demonstrated 79 per cent efficacy at preventing symptomatic Covid-19 and 100% efficacy at preventing severe disease and hospitalisation.
“Vaccine efficacy was consistent across ethnicity and age. Notably, in participants aged 65 years and over, vaccine efficacy was 80 per cent,” the company said.
The interim safety and efficacy analysis announced on Monday is based on 32,449 participants, accruing to 141 symptomatic cases of Covid-19.
The US results come at a time when there is concern over instances of blood clots among some European beneficiaries vaccinated with the AstraZeneca shot. The company said the safety board had specifically conducted a review of the thrombotic events, and found no risk during the US trials.
“The vaccine was well tolerated, and the independent data safety monitoring board (DSMB) identified no safety concerns related to the vaccine. The DSMB conducted a specific review of thrombotic events, as well as cerebral venous sinus thrombosis (CVST) with the assistance of an independent neurologist. The DSMB found no increased risk of thrombosis or events characterised by thrombosis among the 21,583 participants receiving at least one dose of the vaccine. The specific search for CVST found no events in this trial,” the company said in its release.
Until now, recipients received a reminder message 28 days after the first dose to visit the centre for their second dose. A recipient had the choice to stretch the second dose to upto 42 days. (Express photo) 
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