Ross Clark

Could the weather affect coronavirus?

Could the weather affect coronavirus?
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What’s new in the world of coronavirus research this week? The most eye-catching study comes from the University of Maryland School of Medicine revealing a possible relationship between coronavirus outbreaks and meteorology. 

While the paper is not yet peer-reviewed and its authors admit that it's ‘speculative’ and must be read with extreme caution, it notes that so far the worst outbreaks of the disease have occurred where the average temperature is between 5 and 11 Celsius and the relative humidity is between 50 and 80 per cent. Wuhan in January fell into this zone as did Northern Italy – and most of western Europe in February. South Korea and Japan were also in this climatic zone. But as I noted here a week ago, the decline of the Wuhan outbreak coincided with an increase in temperatures there.

Moreover, the disease has been detected, but then failed to take a hold, in several places where temperatures and humidity have been outside the 5 to 11 Celsius range. It has barely spread into northern China and Mongolia (too cold), and neither has it erupted yet in places like Hong Kong, Singapore, and Vietnam, despite cases being discovered there early on in the outbreak. The latter have all predominantly been warmer than 11 Celsius. As for Madrid – where the worst outbreak has been in Spain – it's in the zone with temperatures of 10 Celsius this afternoon. Barcelona and other coastal cities are warmer.

Obviously there are many other factors in the spread of the virus: the response of healthcare systems, government measures to halt the spread of the virus, connections with countries which have suffered from the disease. Yet how viruses spread is known to respond to temperature. That is why we talk of ‘seasonal flu’ – because it advances and then retreats every year. Laboratory tests have shown how the survival of other coronaviruses is highly related to temperature. In one study a coronavirus was found to survive for up to 48 hours on a steel surface at 20 Celsius but only between eight and 24 hours on the same surface at 30 Celsius.

The good news is that new cases of Covid-19 ought to decline as the weather warms in the northern hemisphere. The bad news is that Britain will remain in the 5 – 11 Celsius zone for longer than Italy or Spain. By late April southern England ought to be emerging from the ‘magic’ zone, but it is highly variable from year to year. In 2017, London and the Solent had mean temperatures of over 10 Celsius for April. In 2018 most of South East England, from the Severn to the Wash, were above this level. But last year nowhere in Britain reached an average of 10 Celsius for the month. In fact, last year few places reached an average of 12 Celsius even in May.