The increasing gap between two Covishield doses in India while the UK reduces its window has laypersons confused, but several experts say there is little reason to worry and second jabs anytime before six months can still be effective boosters.

The government last week extended the gap between two doses of the Covishield Covid-19 vaccine to 12-16 weeks, up from the previous maximum of eight weeks, on the recommendation of the National Technical Advisory Group on Immunisation (NTAGI).

A day later, UK cut the gap from 12 weeks to eight weeks in view of the spread of the B.1.617 variant that originated in India. Responding to concerns that India increased the gap primarily because vaccines were in short supply and many states had complained of acute shortage in supplies, immunologist Rath said vaccine dosing is "quite flexible and forgiving". Once four weeks have passed, the next dose can be taken whenever practicable, until six months.

According to the scientist, vaccine doses will be safe no matter when they are taken but will not provide any great "boosting" if given within less than a month or so of the previous dose. "So vaccine doses can be taken any time after at least four weeks have passed from either the first dose or after an actual episode of Covid-19," Rath, from New Delhi's National Institute of Immunology (NII), said. "Secondly, vaccine doses will give perfectly good boosting if given any time up to as much as six months or so after a previous dose. So a second dose, or the first dose after a COVID19 episode, does not have to be taken after four weeks," he explained.

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