India is emerging from the worst of its coronavirus epidemic, with no sign of a second wave in sight. The country with the second largest population in the world has been slowly easing lockdown restrictions since May 2020, but is recording fewer than 100 daily covid-19 deaths on average. This is in contrast to the peak in September, when there were 10 times that number.
Since the first case of covid-19 was reported in the country on 30 January 2020, India has recorded more than 10 million coronavirus infections. But the pandemic is slowing down in India, hitting a low of just 8635 new covid-19 cases reported on 2 February, as opposed to the staggering 97,894 new cases reported on 16 September 2020, amidst the peak.
In contrast to many other nations, including the UK, India has only seen one distinct wave of covid-19 infections.
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One potential explanation, fuelled by the by researchers at Maulana Azad Medical College, is that enough people now have immunity for the virus鈥檚 spread to be quelled, known as herd immunity.
The random survey tested 28,840 people in Delhi and found that 56 per cent of samples contained antibodies against the coronavirus. The figure reached 62 per cent in one district. This is considerably higher than the first such survey in Delhi last July, which detected antibodies against the coronavirus in just 23 per cent of samples.
However, the snapshot from Delhi is unlikely to be representative of the country as a whole. A by the Indian Council of Medical Research showed that just 21.5 per cent of adults in India have antibodies against the coronavirus, according to a newspaper report from 4 February, notably lower than the level of so-called seropositivity seen in Delhi. The survey tested 28,589 adults across 21 states between 17 December and 8 January.
鈥淚t is implausible to infer that the entire country has reached herd immunity due to the diverse nature of every region and populations within India,鈥� says Giridhara R. Babu at the Public Health Foundation of India (PHFI).
鈥淭here are differences between urban and rural areas, slums and non-slums, well-developed districts and less-developed districts which lead to different levels of exposure to the virus,鈥� says K. Srinath Reddy, also at the PHFI.
Densely populated urban areas, such as Delhi, may have high levels of immunity because there are more opportunities for the virus to spread. Dharavi in Mumbai 鈥� one of Asia鈥檚 largest slums, with a population density 10 times that of Manhattan in New York 鈥� had an as early as August last year, while in rural districts in the Indian state of Haryana it was just 11.4 per cent in October.
The threshold needed to reach herd immunity is unclear. Although some estimates say that between 60 and 70 per cent of a population need to be immune to the coronavirus to achieve herd immunity, the recent outbreak in Manaus suggests otherwise.
鈥淢anaus in Brazil reveals that even a seropositivity of 76 per cent does not confer herd immunity as the pandemic continues to rage there,鈥� says Reddy.
The antibody tests also aren鈥檛 ideal at measuring long-term immunity. 鈥淪eropositivity declines over time, so it is not the best measure,鈥� says Sunetra Gupta at the University of Oxford.
Although it has been estimated that the presence of antibodies against the coronavirus will confer immunity for , but it is unclear how long they will last as the presence of antibodies often wanes over time.
Restrictions such as curfews, mandatory face coverings and a test-and-trace system should have played a part in lowering case numbers, but similar measures are in place in most countries.
The lack of a second wave in India doesn鈥檛 seem to be an artefact of statistics, either. India currently conducts 499 daily covid-19 tests per million people, with approximately 1.7 per cent of these testing positive on average. 鈥淚t is quite clear that the decline is not due to a decline in testing,鈥� says Jishnu Das at Georgetown University in Washington DC.
A feasible explanation for the decline in cases and deaths related to the coronavirus is India鈥檚 relatively young population. Half of the population is under 25, and just 6 per cent are over 65, compared with 18.5 per cent in the UK. Age is a major factor increasing the risk of catching covid-19, having more severe symptoms and even death, with the majority of covid-19 fatalities occurring in people over the age of 65.
In India, there may be widespread infection in younger groups, who are more likely to experience milder symptoms and have lower mortality rates, says Babu.
Some epidemiologists suggest that widespread exposure in India to other human coronaviruses, which cause common colds, may infer a . Such exposure could leave people with T-cells 鈥� components of the immune system that recognise and kill infected host cells 鈥� primed to respond to this new threat.
鈥淭here is evidence that there is cross-protection between the different seasonal coronaviruses,鈥� says Gupta. 鈥淚t may be that these populations of high density, where the prevalence of the coronaviruses is higher than other countries, are better protected.鈥�
If this is the case, the threshold needed to reach herd immunity in India would be lower than expected, she says. It would mean that a proportion of the population would already have cross-immunity protection against covid-19 from exposure to other coronaviruses 鈥� and it could be this that has prevented a second wave in India.
Still, it is unclear whether India will avoid a second wave. The country has vaccinated over 9 million people against covid-19, but that leaves more than 99 per cent of the population still to go. And with shopping centres and other public facilities fully , after nearly a year of restrictions, social distancing measures still need to be in place to minimise the spread of covid-19.
This is especially the case given the emergence of new variants that could evade vaccines. The quick-spreading coronavirus variants first spotted in the UK, Brazil and South Africa have all been .
鈥淲e have to remain vigilant,鈥� says Preeti Kumar at PHFI. 鈥淲ith so many imponderables, it will be dangerous to drop our guard.鈥�
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