The government said the gap between the two doses of Covishield should be 12-16 weeks.
Increasing the gap between Covishield doses was a decision based on science, not vaccine shortage, says a member of the group that recommended the big change. The government has launched a detailed study to compare the benefits of increasing the dose gap, said NK Arora, chairman of the Covid working group.
Yesterday, the government said the gap between two shots of Covishield should be 12 to 16 weeks. It had been four to six weeks to start with, and had been widened to six to eight weeks.
Dr Arora, who is a member of the National Techincal Advisory Group on Immunization, rejected speculation that the decision was spurred by vaccine shortage that has halted inoculations of those between 18 and 44 in parts of the country.
"If I increase the gap by one month, then what difference will it make? It will make a difference of about four to six crore doses. So giving the second dose after a month is hardly going to address vaccine shortage. Increasing the gap is beneficial," he told NDTV in an exclusive interview.
According to him, there was new scientific data that if the second dose of the Oxford AstraZeneca vaccine - called Covishield in India - was given after three months, then the chances of protection from infection is 65 to 88 per cent.
"Initial studies on the vaccine had even talked about a 44-week gap. Canada has made it four months," he said.
Dr Arora said antibodies to fight the virus increased substantially after the second dose, but the degree of their impact was not yet known. "But data shows if the gap is increased, the antibodies increase by 40 to 50 per cent," he explained.
Yesterday's announcement has predictably led to concerns among those who took the Covishield doses within the previously prescribed one month gap.
"Those who have taken the shots within a one or two month gap do not need to worry. The production of antibodies will be good."
On comparing the effectiveness of the vaccine for a 28-day gap, a four-six week gap or 12 to 16 week gap, Dr Arora said there was no data so far but the government had planned a study.
"How much protection will increasing the gap give? How much will it protect from the severity of infection or death? In the next four weeks, data of this study will start coming and will be released in regular bulletins," he disclosed.
Data so far revealed a 0.02 to 0.04 per cent chance of reinfection after both doses, said the top expert, and the chances of a severe infection or death were "very rare".
According to him, around 95 per cent of adverse effects after full vaccination were mild and only a fraction was severe. "But our data has shortcomings. Most adverse impact cases are reported only in the first three-four days. We have asked for data on problems experienced even after 28 days."
On cases of death after both shots, Dr Arora said these were still being examined.
"We have to see whether those are from Covid or from the vaccine. We don't know much about Covaxin yet but from international reports, we know that there can be problems four to 20 days after a Covishield shot. There could be clotting or bleeding. We haven't seen this problem here so much, only about 0.61 per cent. About six persons in a crore can experience clotting or bleeding. That is far less than European numbers," he said, asserting that the vaccines were completely safe.
He said the reason why door to door vaccinations had not been allowed was because in case of a severe allergic reaction, if there was no immediate treatment, it could cause death.
Dr Arora said as far as plasma went as a Covid cure, "one should not be over-enthusiastic" about it as in India, it has been seen that patients don't really benefit that much.