Indias daily coronavirus infections have fallen almost 20 per cent over the past three weeks, raising hopes that the pandemic may be peaking in the cities that were among the hardest hit in the world.

The seven-day rolling average of new daily cases in india peaked at 93,300 in mid september. that average has now dropped to 75,000 new cases a day.

But epidemiologists are cautious, noting that the virus was spreading from big cities into smaller towns and rural areas that have weaker healthcare systems and far less testing capacity.

There is a real declining number, but how sustained this decline will be can be debated, said rijo john, a health economist at the indian institute of management, kozhikode. will it be sustained or not? that is the thing to look at. i fear it will not.

India has recorded more than 6.9m coronavirus infections more than any country except the us and more than 106,500 covid-19 deaths since the start of the pandemic, which has battered the economy.

However, bhramar mukherjee, a professor of biomedical statistics at the university of michigan, believes indias official coronavirus numbers are just a fraction of the countrys actual infections. she estimates that more than 100m indians have been infected.

Millions more are at risk of falling ill in the coming months, she said, given new delhis apparently limited appetite and capacity for containment and its determination to revive its stricken economy.

Indias seroprevalence, the percentage of the population that has antibodies indicating exposure and immunity to the disease, is estimated to be less than 7 per cent. its going to be a long haul for india, ms mukherjee said. as soon as you let your guard down, the caseload is going to come soaring up.

Experts think that big indian cities such as mumbai, new delhi, chennai and pune could have reached a turning point, although they worry that this months festival season could stoke a surge in new cases.

There are urban centres which really have a high prevalence of infection, which would suggest these cities might be reaching, or pretty close to, herd immunity. you might not be seeing higher numbers from these places, said mr john.

Recent studies found nearly half of punes population, a third of mumbai residents and nearly 30 per cent of delhi residents have antibodies indicating exposure to the virus.

As more and more people get infected, the number of susceptible people in the population declines and that is why outbreaks slow with time, said shahid jameel, chief executive of the dbt/wellcome trust india alliance, a biomedical research charity.

But as the virus circulates in the hinterland, fewer infections are likely to be found and counted.

People [in] villages and rural districts have less opportunity to be tested because they dont have testing facilities, so even if they are infected you wouldnt know, mr jameel said.

But he also pointed out that the virus would probably spread less rapidly in rural areas owing to their lower population density.