In November 2020, Dr. Ajeet Jain in New Delhi felt like living in a nightmare when the hospital was full of Covid-19 patients, but three months later, the situation was completely different.

Three months ago, hundreds of patients at Jain's hospital were admitted to the intensive care unit.

"We breathed a sigh of relief," said Jain.

India recorded its first case of nCoV infection on January 30, 2020 and its first death in mid-March 2020.

The number of deaths then began to decline.

Experts have warned that nCoV will wreak havoc on the populous cities of India due to poor sanitation.

The government sought to halt the virus early, halted international flights and imposed one of the world's most stringent blockade orders in March.

However, the restrictions have been gradually eased since June 2020 as the government sought to boost the pandemic-devastated economy.

Epidemiologists in India say there is a possible explanation for the decline of new infections: Viruses are more difficult to spread because a significant portion of the population, at least in cities, is infected with nCoV.

Experts say that the number of people with nCoV in India may be much higher than official figures.

In New Delhi, one of the hardest hit cities, serological data released this week showed that more than half of the 28,000 sampled people developed antibodies.

The major Indian cities have probably "reached the threshold of population immunity," said Giridhar Babu, an epidemiologist at the Public Health Organization of India.

However, there are mixed opinions around the question of whether public immunity has emerged in much of India.

World Health Organization regional director Poonam Khetrapal Singh praised the Indian people wearing masks, keeping distance and hygiene, saying that these have proven effective in curbing transmission.

But she added: "India is such a large and diverse country, it is difficult to attribute the reduction to public immunity."

Meanwhile, India is rapidly rolling out vaccination with an ambitious goal of vaccinating 300 million people by July.

A study published in the Lancet last week found that nCoV flare-ups in the city of Manaus, Brazil, have been severely affected, despite the high proportion of people with antibodies.

Some of the reasons given include impaired immunity from a previous nCoV infection and a new stronger variant.

"We can't let our guard down," Singh said.