STEVE INSKEEP, HOST:
India has some mysteriously good news. Last fall, India looked likely to overtake the United States as the country most infected by coronavirus, but the number of COVID-19 cases confirmed in India has recently plummeted. Scientists want to know why. NPR's Lauren Frayer reports from Mumbai.
(SOUNDBITE OF CAR HONKING)
LAUREN FRAYER, BYLINE: Ooh, took that pothole - my rickshaw driver is careening around. Red lights seem to be - yeah, straight. Red lights seem to be a mere suggestion to him. But he's wearing a mask and so am I. That's the reason I sound muffled. Police could pull us over and give me a ticket - a 200 rupee fine - for riding without a mask.
GENEVIE FERNANDES: Very stereotypically, we are known to break the rules as you see traffic rules being broken. But in this particular case, the police, the monitoring, enforcement, that was ramped up. Every time they fine a person 200 rupees, they also give them a mask to wear.
FRAYER: Health policy expert Genevie Fernandes says mask mandates are one of the things that may have helped reduce India's COVID-19 caseload. Whenever you make a phone call here, instead of a ring tone...
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AMITABH BACHCHAN: (Non-English language spoken).
FRAYER: ...You hear recordings like this one from Bollywood legend Amitabh Bachchan urging you to wash your hands and wear a mask. There's also the heat and humidity. There is some evidence they may reduce the virus' spread. Dr. Daksha Shah is a government epidemiologist.
DAKSHA SHAH: The temperature, of course, is in the favor. We do not have too much cold climate over here. So many of the viruses, they are known to multiply more in the colder regions. In addition, inherent immunity to so many infections already exists in the population.
FRAYER: Malaria, typhoid, dengue fever are all endemic in India. People with robust immune systems are more likely to survive here in the first place, Shah says. Plus, more than half of the population is under age 25. They're less likely to die of COVID and more likely to get it asymptomatically. But India's climate and demographics have not changed during the pandemic, and the drop in cases here has been recent. In September, India was reporting nearly 100,000 new infections a day. This month, there was a day with just 10,000. This is in a country of nearly 1.4 billion people.
JISHNU DAS: It's not that India is testing less or things are going underreported and it's been rising, rising, and now suddenly it's vanished. I mean, the hospital ICU utilization has gone down. Every indicator says the numbers are down.
FRAYER: Health economist Jishnu Das says the numbers went down exactly when we thought they would spike - in October, when people gathered for the Hindu festival of Diwali. Shah, the epidemiologist, wonders if just like a more infectious variant was discovered in the U.K., maybe a less infectious variant has mutated in India.
SHAH: Maybe some processes must have happened. This is an evolution of the virus itself. We need some more deeper evidence and deeper studies.
FRAYER: The truth is that scientists don't yet know. Here's Das, the health economist again.
DAS: Three options. One is it's gone because of the way people behaved. So we need to continue that behavior, right? It's gone because it's gone and it's never going to come back - great. Or it's gone - we don't know why it's gone and it may come back.
FRAYER: So for now, Indians are kind of holding their breath, just doing what they're doing until they get vaccinated. Lauren Frayer, NPR News, Mumbai.
(SOUNDBITE OF ODESZA'S "LIGHT (INSTRUMENTAL)") Transcript provided by NPR, Copyright NPR.