NEW DELHI (REUTERS) - India said on Thursday (Jan 28) that it had curbed an increase in Covid-19 infections, with a fifth of its districts reporting no new cases for a week, even as its immunisation campaign has covered 2.4 million people.

The country of 1.35 billion has recorded the highest number of cases in the world after the United States, though the rate of infection has come down significantly since a mid-September peak. Some studies have suggested pockets of India have attained herd immunity through natural infection.

"India has successfully contained the pandemic," Health Minister Harsh Vardhan said, noting that fewer than 12,000 cases were reported in the past 24 hours. He said 146 of India's 718 districts have had no new cases for a week, and 18 districts for two weeks. "India has flattened its Covid-19 graph," he added.

The world's second-most populous country started its Covid-19 immunisation programme on Jan 16, with the aim to reach 300 million people by July-August.

India has so far reported 10.7 million infections and 153,847 deaths - one of the world's lowest fatality rates from the disease, attributed partly to its younger population.

Thyrocare Technologies, one of India's top three diagnostic chains, told Reuters that antibody tests it had done on more than 700,000 people showed that 55 per cent of the country's population may have already been infected. The World Health Organisation says at least 60 to 70 per cent of the population needs to have immunity to break the chain of transmission.

A top Indian vaccine official told Reuters he did not think India had reached that level yet, but that even a smaller percentage could help slow the spread of the virus.

"Most of our highly populated districts and cities have had their run of the pandemic by now... and may have what you like to call herd immunity, to an extent," Mr Vinod Kumar Paul, who heads a committee on vaccine strategy, said earlier this month.