The Centre’s “75-day” offer of free Covid-19 vaccine booster doses closed on Friday with over 70 per cent of eligible adults in the country not turning up for the jab.

The free booster campaign, over 78 days from July 15 to September 30, raised the “precaution dose” coverage for eligible adults to 27 per cent, the Union health ministry said.

During the campaign, more than 150 million eligible adults received booster doses at designated hospitals and at more than 11,000 camps at bus stations, 5,600 camps at railway stations, and over a million camps in private and government workplaces.

Over 95 million people aged between 18 and 45 years had received precaution doses up to September 29, according to the ministry’s daily vaccination update, implying an 18-fold rise from the 5.2 million that had taken the precaution doses up to July 15.

The count of people between 45 and 60 years who have taken their boosters has increased 12-fold — from 3.7 million up to July 15 to 48 million on September 29. The booster coverage for those aged 60 years or older has increased from 27 million on July 15 to 47 million on September 29.

Despite the improved coverage, the vaccine update suggests that large proportions of eligible adults have not opted for boosters yet. More than 515 million in the 18-45 age group have received second doses, but only 95 million have taken boosters.

The health ministry has said the administration of the precaution dose — the term the Centre has used for booster doses in India — “is pivotal” to conferring full and extended protection to beneficiaries against Covid-19. It helps reduce the severity of the disease and risk of hospitalisation.

Even among those 60 years or older, who are at higher risk of severe disease than younger people, many have not taken boosters yet. Among 123 million in the 60-plus age group who have received second doses, only 47 million had taken boosters up to September 29.

Health experts say that booster doses are needed given the continued circulation of the coronavirus, currently driven by sub-lineages of the omicron variant that had caused India’s third wave during January this year.

The country’s coronavirus epidemic has continued to shrink since a relatively mild surge in summer this year, the seven-day average of daily new cases falling from nearly 20,000 in late July to 4,000 in late September. The current seven-day average of daily deaths is around 20.

Public acceptance levels for boosters in India have been conspicuously lower than the exceptionally high acceptance rates for the two vaccination doses. Experts say the reason for the low booster uptake is unclear but perceptions of low risk and the low daily counts of Covid-19 have likely contributed to it.