The TLDR: While the virus surges in great parts of the world—mutating unchecked—India’s cases have been steadily declining, and for no apparent reason. We look at the various theories put forward to explain this seeming miracle.

First, the numbers

• The number of daily new cases has fallen precipitously from 100,000 in September to 8,635 as of February 1. 
• The number of daily deaths is below 100 for the very first time since May. 
• And our mortality rate—percent of cases that end in death—is only 1.44%, way lower than the US, UK and other European countries.
• Our positivity rate—the percent of tests that turn up positive—has dropped from 11.7% in August to 1.7% in January. This is typically taken as a sign that the pandemic is receding.

The exceptions: Kerala and Maharashtra—while their number of active cases remains high, but even here the totals are falling. 

Our pandemic chart currently looks like this:

As a health economist told NPR:

"It's not that India is testing less or things are going underreported… It's been rising, rising—and now suddenly, it's vanished! I mean, hospital ICU utilization has gone down. Every indicator says the numbers are down."

Point to note: In most parts of the country, people are out and about—and daily life has returned to near normalcy for most Indians. So we’re not staying safe at home either—even if travel etc remain below pre-pandemic levels.

So what’s with this sudden vanishing?

Theory #1: Mandatory masking

This is one of the popular theories advanced to explain our lower numbers compared to, say, the US—where masking has been a source of continual conflict. NPR suggests that the government policy that made it mandatory to wear a mask in public (accompanied by heavy policing) may have worked—far better than the total lockdown. 

OTOH, as leading virologist Gagandeep Kang points out, “If you look at the places that did well with control early on, they are the ones [that] have a high level of infection now.” This includes states like Maharashtra, Gujarat, Karnataka, Delhi that have been the most diligent. So maybe not…

Theory #2: Herd immunity

This is the most persuasive argument for our declining numbers. Herd immunity is when a certain percentage of the population is infected with the virus, it can no longer jump from one person to another with ease—and eventually dies out. This can be achieved either through the natural spread of the disease, or via vaccination. This is what it looks like:

Point to note: In the early days of the pandemic, scientists set 60-65% as the threshold for herd immunity. But later estimates have revised that downward to 35-48%.

Poverty as a  blessing? Unlike folks in the West, Indians simply couldn’t afford the luxury of social distancing. For example, urban slums where residents live cheek-by-jowl—and migrant workers who traveled long distances by foot or on crowded trains to reach home.

“[U]rban slums were perfect places for the virus to spread quickly, lockdown or no lockdown. In fact, a vast number of poor migrant workers trapped in these slums could have only meant exposing them quicker to the infection… It was then not surprising that a large number of them were infected, before they were even allowed to go back to their homes.”

As a result, the virus spread unchecked across the country—spreading even further when the lockdown was eased. Virologist Jacob John says:

“What we seem to have done is let the virus run its course… By not flattening the curve in the beginning, India went through the herd immunity threshold and the epidemic seems to be naturally coming down.”

The numbers: certainly support this theory. The latest national sero-survey—which reveals how many people have been exposed to the virus—suggests that the number of actual infections may be as high as 320 million. That’s 30x the official number of 10.7 million lab-confirmed cases. So that’s roughly one in four Indians.

In sero-surveys conducted in big cities, those numbers are even higher: 50% in Mumbai, 56.3% in Delhi, 60% in Pune and 30% in Chennai. A model developed by IIT scientists suggests that 55% of all Indians may have been infected as of December. The most shocking finding:

“Our model shows that the disease prevalence in Bihar has reached as high as 65 per cent. In fact, for every confirmed case of infection, there might be 300 that are unreported. This ratio is the highest in Bihar. Now, if that is true, it would be able to explain why Bihar is reporting only about 500 cases a day."  

Point to note: Big nationwide percentages tell us very little about whether India has achieved herd immunity—because the virus has not spread in a uniform fashion. Experts caution:

 “What we are seeing is a complex mixture of high exposure in densely populated areas (cities) where the outbreak also moves faster, and low exposure in villages and rural districts where the outbreak may still be expanding, but doing so slowly.”

Also this: Not all Indians have been out and about, and they remain as susceptible as ever:

“Most of the country’s 270 million schoolchildren have not set foot in a classroom since March, though some states have allowed a limited number of older students to return. White-collar professionals have mostly worked from home for 11 months, while many elderly Indians have scarcely stepped out at all, with the likelihood that they remain susceptible to infection.”

Theory #3: India is unique

There are a number of theories that point to ‘only in India’ factors:

We are young: More than half our population is under the age of 25—which means they are less likely to die of the disease and more likely to be asymptomatic. Also, just 6.5% of India’s population is over 65 years old—compared to 20% in Europe.

A hot and humid country: Our climate is inherently inhospitable to the coronavirus since even our winters are not severe. This is somewhat borne out by a study in Punjab that found that 76% of patients there did not infect a single other person. As NPR notes:

"A review of hundreds of scientific articles, published in September in the journal PLOS One, found that warm and wet climates seem to reduce the spread of COVID-19. Heat and humidity combine to render coronaviruses less active—though the certainty of that conclusion, the review says, is low. Previous research has also found that droplets of the virus may stay afloat longer in air that's cold and dry.”

Also this: most of us can’t afford air-conditioning—which accelerates the spread of the virus. And most Indians in rural areas are mostly outdoors. OTOH, we have high levels of air pollution which should (in theory) heighten the risk of infection. 

Our bodies are accustomed to disease:  This is a point of debate, but some leading virologists like Gagandeep Kang advocate this theory:

“We are seeing a lot less severe disease than the rest of the world, and a lot more asymptomatic infections… Part of the reason might be prior exposure to lots of other pathogens… We live in an environment where we are exposed to all kinds of pathogens all the time and we learn not to react too much.”

Two preliminary studies out of India suggest this may be true. One found that low- and lower-middle-income countries with less access to health care facilities, hygiene and sanitation have lower numbers of deaths per capita. The other attributes the lower fatality rate to exposure to “a diverse range of microbes and bacteria.” But neither have been peer-reviewed.

OTOH, others in the field vehemently disagree—and say there isn’t much difference between our mortality rates and that of others in South and Southeast Asia.

“‘Once we account for differences in age structure of population, there is not much difference in case fatality rates across countries, if measured correctly,’ [epidemiologist Ramanan] Laxminarayan said. [Immunologist Satyajit] Rath concurred with Laxminarayan, saying there is no strong clear evidence that the illness is less severe in India compared to elsewhere. ‘I see no reason so far to invoke speculation about ‘better immunity’ or any genetic resistance in India. I have seen no evidence for either of those possibilities,’ he added.”

A weaker mutation: This is the outlier among all the theories. The speculation is that a less infectious variant of the virus may have spread across India. But it is mostly speculation since we have tracked the genetic sequence of the virus until recently—when worries about the UK variant triggered a sudden scramble.

Another outlier: The BCG vaccine—which is given to kids to protect them from tuberculosis. The government-run Indian Council of Medical Research is conducting a study to test the effects of the vaccine on the elderly. Initial results show that it offers a boost to their immune system—but there is no evidence that it protects against the virus.

The bottomline: The declining case count is not entirely a blessing. For one, it makes it harder to conduct vast stage 3 trials for vaccines that are still being tested. Worse, it leads to greater complacency—at a time when we are not doing much to guard against new and more infectious variants. Scientists have identified escape mutants in Andhra Pradesh and are looking closely at mutations in cases in Kerala. So we’re not exactly out of the woods. As one expert told Financial Times:

“A lot of this is in the rear-view mirror but that doesn’t mean we are done and dusted yet… We have an artificial situation in which we’ve reached an equilibrium, but if we went back to normal, there is still a lot of room for cases going up.”

Reading list

NPR and Financial Times (paywalled) have the best reporting on the subject. The Print’s op-ed uses the declining cases—and evidence of herd immunity—to take aim at the severe lockdowns. Hindustan Times talked to experts who flag our rosy assessments of our mortality rates. We explained how herd immunity works here.