Seasonal effects

There’s been plenty of speculation (here, here, here,…) that the novel Coronavirus might be seasonal, meaning that transmission rates will reduce significantly in the warmer summer months in temperate countries. This would help significantly in controlling the current epidemic wave, potentially buying considerable time in allowing vaccine development or other exit strategies from current lockdown conditions.  But so far there’s been little direct evidence that the Coronavirus is genuinely seasonal.

However, the following tweet links to a statistical analysis which, though circumstantial, provides reason to believe in a seasonal effect. The author of the study looked per-capita death rates due to COVID-19 in individual counties of the United States. They then fitted a regression model using demographic and climate-based statistics as potential explanatory variables for differences in county-to-county rates. What emerged is that temperature is the most significant factor. That’s to say, after allowance for other explanatory factors, the one that had the most impact was temperature: in counties with higher average temperature, everything else being equal, the per-capita death rated to COVID-19 was lower.

Of course, there are all sorts of caveats – see discussion here –  about extrapolating from the conclusions of the type here to assuming seasonality in the worldwide transmission behaviour of the virus. But it is, at least, another reason to be cheerful optimistic.

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