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Blood clots in colder climates could be why India has fewer Covid deaths than West, study says

A study in IJMR by a team at Homi Bhabha National Institute found that Covid cases in colder climates are more likely to develop blood clots, which increases the risk of death.

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New Delhi: Researchers from Mumbai have suggested there may be an association between seasonal and geographical variations and Covid-19 deaths, based on a Chinese study and a comparison of fatality data from countries across the world.

In an article published Friday in the Indian Journal of Medical Research (IJMR), a team from the Homi Bhabha National Institute in Mumbai suggested that the underlying pathology, which is more prevalent in colder climates, may partially explain India’s low Covid-19 mortality rates in comparison to that of Western countries.

In the paper, the team explained that reports from China, the US and Europe suggested that venous thromboembolism — a condition in which a blood clot forms in the veins of the leg, groin or arm — is an important cause of death in Covid-19 patients.

These blood clots circulate through the veins and get lodged in the lung, preventing a healthy exchange of oxygen and carbon dioxide in the lungs, which increases the risk of death.

Earlier attempts to draw correlations between the number of infections and seasonal variations saw scientists speculate that Covid-19 spread is slower in warmer climates. However, as the disease progressed and summer approached, the infection continued to spread. Studies also showed that heat and humidity did not curb the spread of the SARS-CoV-2 virus that causes Covid-19.

Also read: Delhi and Mumbai’s high Covid tally linked to severe air pollution levels, say experts

What the latest research says

The team, which includes Rajendra A. Badwe, Rajesh Dikshit, Pankaj Chaturvedi and Sudeep Gupta, said that comparisons of infection numbers between countries is unreliable because the number of cases identified can vary with the number of tests conducted.

Instead, they said the number of deaths are better documented and hence are a more reliable metric for comparisons.

The authors pointed to a study from China which concluded that venous thromboembolism is less prevalent in warmer climates.

This indicated that people in colder climates are more predisposed to develop venous thromboembolism. Similarly, people living closer to the equator are less likely to develop this condition compared to those living in warmer climates.

This seasonal variation of venous thromboembolism may be linked to antiphospholipid antibodies, a type of protein that is mistakenly produced by the body, damaging cells and causing blood clots to form in the veins and arteries.

According to the authors, the role of these antiphospholipid antibodies in Covid-19 is yet to be understood.

But these observations suggest that seasonal and geographical variations in the antiphospholipid antibodies and venous thromboembolism could reduce Covid-19 mortality in warmer conditions, the researchers stated.

“It is likely that other differences such as those in age, comorbidity burden and other as yet unknown factors could account for the difference in population-level mortality between India and Western countries,” the researchers said in the paper.

This paper is not based on experimental findings conducted by the author, but rather a ‘viewpoint’ based on existing data and research.

The authors say that more long term data is needed to draw a more definitive conclusion about the link between climate and Covid-19 mortality.

Also read: Climate change is set to become worst crisis of our time. Covid recovery could change that


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  1. Rubbish argument about blood clot. It’s the English medium education of Librandus that saves lives in India. Mother tongue education can only produce fools to do idol worship.

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