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Tuesday July 27th, 2021
Health

How are COVID-19 cases in South Asia suddenly on the decline?

Covid-19 lockdown community lunch – Image by Rajesh Balouria courtesy Pixabay

ECONOMYNEXT – New COVID-19 cases in India have plummeted from a peak of 90,000 a day in September to just over 10,000 in February. In Bangladesh, daily cases have dropped to a 10-month low. The number of active cases in Pakistan has decreased by some 20,000 over the last two months. Life is almost back to normal in Kathmandu, Nepal. Bhutan has been called the world’s unlikeliest pandemic success story. What’s going on in South Asia?

India’s numbers in particular have baffled some scientists. Just over six months ago there were very real concerns that the “fragile” healthcare system there would collapse under the weight of the raging pandemic. Fast forward to February 2021 and daily cases have dropped significantly. According to CNN, on February 9, Delhi reported zero virus deaths for the first time in nearly nine months. Contrast that to how dire things were in November last year when nearly 90% of all critical care beds with ventilators in New Delhi were full. The Associated Press (AP) reported that by the second week of February only 16% of these beds were occupied.

Credit: BBC

What has led to this dramatic change? Is there something unique about South Asia that might explain its sharply declining cases and relatively low mortality rates? Is it vaccination? Is it the climate? Is it something in the water?

A number of explanations have been put forward: The country’s (and by extension the region’s) younger population, a partial herd immunity in urban areas, under-reporting of cases and deaths, reduced testing, increased restrictions, and relatively better innate immunity owing to a higher incidence of other infectious diseases.

The Indian government, according to AP, has attributed the dip in that country’s cases to mandatory mask-wearing. But this does not explain how the decline appears uniform even in areas where mask-wearing is not strictly practiced. Under-reporting, meanwhile, does not explain the demonstrably reduced stress on India’s health system. The dip cannot be attributed to vaccination either, which began only in January.

The threshold for herd immunity for COVID-19, experts say, may be 70% or higher, which means a vast majority of the population need to have developed immunity to the virus either by getting infected or through vaccination. A serological survey that tested for antibodies in January found that more than half the population in Delhi had contracted the disease.

“This is a huge increase,” community medicine specialist Dr Hemant Shewade was quoted by CNN as saying. He added that big cities may see “considerably reduced” transmission due to the rise in immunity.

While there may be some herd immunity in urban centes, India’s total numbers are far below the 70% required to achieve national herd immunity. According to AP, only about 270 million, or about 20% of the population, had been infected by the virus before vaccination began.

Serum Institute of India CEO Adar Poonawalla was quoted by CNN as saying India might not achieve herd immunity for years. “Until you get that real magical 90% herd immunity or vaccine immunity, which will come after three or four years, you really should exercise precautions,” Poonawalla, whose company is the largest manufacturer of COVID-19 vaccines in India, told CNN in January.

Rural areas with lower population densities and therefore reduced transmission rates have reported fewer cases of infection, which may at least partly explain the nationwide decline. Another, perhaps more intriguing, possibility is the idea that the prevalence of infectious diseases such as cholera, typhoid and tuberculosis could have helped build a stronger initial immune response to the new virus.

Shahid Jameel, a virologist and director of Ashoka University’s Trivedi School of Biosciences told AP on February 16: “If the COVID virus can be controlled in the nose and throat, before it reaches the lungs, it doesn’t become as serious. Innate immunity works at this level, by trying to reduce the viral infection and stop it from getting to the lungs.”

What of the low mortality rates in the region? A study published in the International Journal of Infectious Diseases attributed this to cross-reactive immunity, which, Dr. Giridhar R. Babu, a Bengaluru-based epidemiologist who was part of the research team, says plays a significant role in reducing the severity of the disease.

”The presence of cross-reactive T cells presumably from prior coronavirus infections can also attenuate the severity of the disease. Another reason for the low mortality is based on the emerging evidence suggesting asymptomatic and mildly symptomatic patients have high SARS-CoV2 specific cytotoxic T-cell responses, ” Bahu told The Week in December.

Meanwhile, one expert in Sri Lanka does not believe there is anything unique about what’s happening in India or elsewhere in the region except perhaps Bhutan, a country that imposed stringent border controls and ramped up testing. Institute for Health Policy (IHP) Executive Director Dr Ravindra Rannan-Eliya told EconomyNext yesterday that, over the past two months, cases have been on the decline  in many developing and developed countries.

“This is not due to vaccination – although a lot of people think this is the case in the USA. You see exactly the same decline in Canada starting January 7, a country that has had much less vaccination than the US,” he said.

Credit: FT.com

Rannan-Eliya, far from being baffled by South Asia’s declining cases, believes the virus “basically won” in India, Pakistan, Nepal and Bangladesh – an outcome he attributes to inadequate testing, ineffective lockdowns and poor contact-tracing and isolation measures.

“If you extrapolate from an infection rate of 30% in India, what this means is that, at the minimum, 0.5 million Indians died. The actual number is probably more than 1 million. It’s a similar situation in the other three countries. When I looked at the data for Pakistan recently, there is very strong evidence that most deaths were not counted. There were also a large number of unreported deaths outside Islamabad and in the poorer provinces. There is probably also going to be a long term health cost also with tens of millions suffering long COVID,” he said.

The virus spread freely through the population resulting in partial immunity, said Rannan-Eliya. In combination with continued restrictions, he explained, this should now be sufficient to bring case numbers down. However, if remaining restrictions such as school closures are now lifted, cases may well go up again.

“Looking forward, the big concern is whether there are any new variants spreading. Genomic sequencing is very limited in these countries, so it’s possible we don’t know yet. Variants could easily reverse this scenario. The most obvious example of this is Manaus in Brazil which achieved 70-80% herd immunity last year, but has now suffered a huge second wave because of a variant that is immune resistant,” he said.

In Kerala, the southern Indian state that had previously done an exemplary job of containing the virus, as of mid-February contributed to nearly 50% of the country’s active COVID-19 cases. A new, more transmissible variant is suspected to be behind the recent surge. A new variant was in fact discovered in the state earlier this week, but according to Indian media, it may not be the culprit.

“I don’t think that these countries are exactly back to normal. They have continuing low levels of transmission, and as immunity wanes or as restrictions are relaxed or both, they may see further small waves. If they get some dangerous variants, then these future waves might not be small,” said Rannan-Eliya.

With regard to climate and innate immunity boosted by exposure to other diseases, he said: “I think temperature certainly, and possibly previous cold virus infections, may have slowed spread, but the impacts would have been small. Bear in mind that the worst infected countries in the world are largely hot countries – Brazil, India, Peru, South Africa, much of Africa, etc. So it’s not a big factor. South Asia can be largely explained using standard epidemiology and considering the serology survey data.”

Reported by Himal Kotelawala (Colombo/Feb27/2021)

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