Scientists are trying to work out why coronavirus cases in India are falling when at one point it looked like the country might overtake the US as the worst-hit nation.
In September the country was reporting some 100,00 new cases per day, but that went into decline in October and is now sitting at around 10,000 per day - leaving experts struggling to explain why.
While the Indian government has been keen to put the apparent success down to its mask-wearing and social distancing laws, few believe these measures alone are responsible for the dip.
Instead, experts believe it may be down to the fact that India's largest cities have reached herd immunity, meaning the virus has moved to rural areas where it spreads slower and where cases and deaths are far less likely to be tested and logged.
A recent survey found 56 per cent of people in Delhi - the country's most-populous city - have Covid antibodies, which is likely to be an under-estimate with 70 per cent required for herd immunity.
Only around 20 per cent of deaths in India are medically certified - meaning 80 per cent do not have an official cause of death - with analysts warning the country may be under-counting its Covid fatalities by two or three times.
India also tests far less than developed nations, with medical experts warnings some states are relying on rapid lateral flow tests that give false-negative results.
The country also has a far younger population than many western nations - with an average age under 30 - and has far lower rates of obesity, which are both major factors in serious Covid infections and deaths.
Comparatively low death rate: India has recorded far fewer deaths per million people than either the UK or the US
India's coronavirus cases appear to be falling rapidly - despite mask-wearing and social-distancing laws being lax - leaving experts to wonder why (pictured, fans at the cricket in Chennai packed together and without masks)
Antibody surveys carried out in Mumbai, India's second-largest city, and Pune also showed antibodies in around 50 per cent of the population, The Times reported.
'The most densely-populated areas are already saturated and reaching the threshold of herd immunity, Giridhar Babu, an epidemiologist at the Public Health Foundation of India, told the paper.
'The virus has now spread to rural areas, but they are not so dense.'
Having a less-dense population means the virus spreads slower, which will naturally bring down daily case figures.
But with access to healthcare in rural India often lacking, it may also mean that many cases and deaths are going undetected.
Testing data for India shows that just 0.5 people per 1000 are swabbed each day - one of the lowest rates among countries that report such data.
More data released in September last year showed that people in rural areas are less-likely to be swabbed than those in cities - meaning that as the disease moves away from urban centres, the number of positive tests appears to decline.
The average number of tests carried out per day has also been falling across the whole of India since mid-December, which could also help to explain why positive test results have fallen.
And even those who are swabbed may be returning false-negative results, with doctors warning in September last year that many states are over-reliant on rapid lateral flow tests, which are unreliable.
Rijo John, a public health policy analyst, also warned that some states are failing to report which kind of tests are being used, further muddying the picture.
'More and more states are moving towards rapid antigen detection tests, which are known to have a high percentage of false negatives and not utilising the gold standard RT-PCR tests to full capacity,' he said.
'It should be made mandatory for all states to report the break[down] of different test types as well as the positives from these.'
Data also shows 80 per cent of Indians die at home, with no national requirement for a cause of death to be given before a body can be cremated or buried.
That has led experts to warn of a 'substantial' under-counting of deaths, with Dr Babu warning the true toll could be two or three times higher than the official count.
The crowds at the test match against England have surprised many viewers in the UK
Scientists are baffled by the relatively low rate of coronavirus infections in India after at one point it looked as though it might surpass the US as the country with the biggest case toll. Pictured: People wear face masks outside a hospital in Jammu, India today
The Indian government has also partly attributed the dip in cases to mask-wearing, which is mandatory in public in India and violations draw hefty fines in some cities. Pictured: A student has their temperature taken outside their college in Srinagar today
But others point to easing pressure on the country's hospitals as evidence that something other than an under-counting of cases and deaths in going on.
Some point to India's young population and relatively low rates of obesity as possible explanations.
The country has an average age of less than 30 with just 15 per cent of adults being overweight and 5 per cent obese, according to 2015 data.
By comparison, the US - which has been hardest-hit by Covid - has an average age of 38 with 32 per cent of adults overweight and 36 per cent obese.
Age and obesity are known to be two of the biggest factors increasing the likelihood that someone will fall seriously ill or die from Covid.
Other theories include that India has been dealing with less-virulent strains of the virus than those found in Europe, the US and parts of Africa.
India suspended all commercial flights in March last year, and while it has been operating 'travel corridors' since July, it has been quick to cut off routes to countries where dangerous new variants have emerged such as the UK.
That could have stopped the country suffering from spikes in infections like that seen in Britain after the so-called Kent Variant emerged, epidemiologists suggest.
Others believe that Indians, many of whom live in unsanitary conditions and suffer repeated waves of infections, have naturally resilient immune systems.
England play cricket against India in Chennai, with the stands full of fans behind them
Jacob John, a prominent virologist at Christian Medical College in Tamil Nadu state, said: '[India suffers] dengue, chikungunya, malaria, typhoid, cholera, dysenteries, influenza, so the "innate immune system" is trained to be on high alert.'
The success cannot be attributed to vaccinations since India only began administering jabs in January, with just seven million out of the country's 1.3billion population jabbed so far.
Experts have cautioned that even if herd immunity in some places is partially responsible for the decline, the population as a whole remains vulnerable - and must continue to take precautions.
This is especially true because new research suggests that people who got sick with one form of the virus may be able to get infected again with a new version.
A recent survey in Manaus, Brazil, that estimated that over 75% of people there had antibodies for the virus in October - before cases surged again in January.