Amid calls for shorter booster gap, experts seek more research, data

There is no urgency to reduce the nine-month gap between the second dose of the covid-19 vaccine and the booster shot and India does not have sufficient local data and evidence to guide any such decision, top vaccine experts told Mint.

Moreover, rising covid-19 infections should not force a knee-jerk reaction of reducing the gap, several scientists said.

Just over 10% of adults have completed the nine months’ period to become eligible for a booster. If the nine-month interval remains, just 35% will be eligible for boosters by July-end, potentially leaving some less protected as immunity wanes, show Mint calculations.

However, India does not have much data to favour a six-month gap over a nine-month gap, experts said. “There is no evidence to argue for or against nine months,” said epidemiologist Chandrakant Lahariya. “In India, there is no evidence on the ideal gap, so any interval would be equally wrong or right.”

Earlier this week, a study by the National Institute of Virology found that antibodies start waning six months after vaccination or infection, making a case for a shorter gap. The Centre is likely to reduce the gap to six months soon after an expert group meeting on Friday, PTI reported this week, quoting sources.

The World Health Organization says a booster “may be considered” four to six months after the second dose of the Oxford-AstraZeneca vaccine , and is “mainly recommended” for high-priority groups. With covid-19 reaching an endemic stage in India, some find the risks rather low. “At the moment, given our infection rate and vaccination, I am not worried enough about the numbers to change any recommendation—with the reminder that I do not know how nine months was decided on,” Gagandeep Kang, a top virologist, told Mint.

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T. Jacob John, a former professor of clinical virology at Christian Medical College, Vellore, said shorter intervals were relevant during high-prevalence periods such as the Delta wave and Omicron wave, to protect high-risk individuals, but India has reached the endemic phase since then. “Nine versus six months is irrelevant now…the urgency for a booster is past,” he added. However, he said a booster was a must to complete the immunization schedule.

If the gap is six months, 34% of adults would become eligible right away. With a sudden surge in demand, the concomitant infrastructure will need to be restored quickly. The average number of vaccination sites operating per day has halved to around 46,000 this month from its January peak as demand faded, show Mint calculations. The two-dose drive is nearing its fag end with around 91% of adults doubly vaccinated.

Going forward, experts called for clarity about the aim of the booster shot to agree on the timeframe, along with concrete data on declining protection in the Indian context. “We need to agree on the purpose (to decide the interval),” said Lahariya. “Is a booster being given to reduce transmission or for protection from moderate to severe disease? If it’s the latter, then boosters can wait.” Kang said it was important to first consider whom we want to protect and against what—infection, hospitalisation, or death—instead of making blanket recommendations.

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