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.
India also has a far younger population than many western countries – with an average age under 30 – and has far lower rates of obesity, with just 5 per cent of adults in that category as of 2015.
Around 80 per cent of Indians also die at home, and with no requirement for a cause of death to be given before burial, most analysts believe the country has under-counted deaths – perhaps by two or three times.
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
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, while the number of daily swabs has been steadily increasing, it currently stands at just 0.5 people per 1000 each day – one of the lowest rates among countries that report such data.
Data released in September last year also showed that access to tests for rural Indians is inadequate – while 75 per cent of the population lives in rural areas, it accounted for just 65 per cent of tests carried out.
Meanwhile urban centres, accounting for 15 per cent of the population, made up 22 per cent of the tests.
The average number of tests carried out per day has also been in decline since mid-December, which could help to explain why positive test results have fallen.
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 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
Experts have suggested many possible explanations for the sudden drop, seen in almost every region, including that some areas of the country may have reached herd immunity or that Indians may have some preexisting protection from the virus. Pictured: A health worker checks the temperature of a commuter at a train station in Mumbai on February 11
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 and the US.
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.
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.’
India, like other countries, misses many infections, and there are questions about how it is counting virus deaths.
But the strain on the country’s hospitals has also declined in recent weeks, a further indication the virus’s spread is slowing.
When recorded cases crossed nine million in November, official figures showed nearly 90 per cent of all critical care beds with ventilators in New Delhi were full. On Thursday, 16 per cent of these beds were occupied.
That success cannot be attributed to vaccinations since India only began administering jabs in January – but as more people get a vaccine, the outlook should look even better, though experts are also concerned about variants identified in many countries that appear to be more contagious and render some treatments and vaccines less effective.
The success in reducing the number of cases cannot be attributed to vaccinations since India only began administering jabs in January. Pictured: A policeman receives a Covid-19 vaccine at the Nair Hospital’s vaccination centre in Mumbai today
Among the possible explanations for the fall in cases is that some large areas have reached herd immunity – the threshold at which enough people have developed immunity to the virus, by falling sick or being vaccinated, that the spread begins to slacken, said Vineeta Bal, who studies immune systems at India’s National Institute of Immunology.
But 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.
Ms Bal, for instance, pointed to 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.
‘I don’t think anyone has the final answer,’ she said.
And, in India, the data is not as dramatic.
People wearing face masks stand in a queue outside the municipal office in Jammu, India, today
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
A nationwide screening for antibodies by Indian health agencies estimated that about 270 million, or one in five Indians, had been infected by the virus before vaccinations started – that is far below the rate of 70% or higher that experts say might be the threshold for the coronavirus, though even that is not certain.
‘The message is that a large proportion of the population remains vulnerable,’ said Dr Balram Bhargava, who heads India’s premier medical research body, the Indian Council of Medical Research.
But the survey offered other insight into why India’s infections might be falling.
It showed that more people had been infected in India’s cities than in its villages, and that the virus was moving more slowly through the rural hinterland.
‘Rural areas have lesser crowd density, people work in open spaces more and homes are much more ventilated,’ said Dr K. Srinath Reddy, president of the Public Health Foundation of India.
If some urban areas are moving closer to herd immunity, wherever that threshold lies, and are also limiting transmission through masks and physical distancing and thus are seeing falling cases, then maybe the low speed at which the virus is passing through rural India can help explain sinking numbers, suggested Dr Reddy.
Another possibility is that many Indians are exposed to a variety of diseases throughout their lives – cholera, typhoid and tuberculosis, for instance, are prevalent – and this exposure can prime the body to mount a stronger, initial immune response to a new virus.