The second wave of the Covid-19 pandemic

Today, I took another look at the second wave of the Covid-19 pandemic using data on confirmed cases downloaded from the Johns Hopkins University CCSE data repository. This post focuses mostly on western European countries, with a few others like USA and Australia included. The plots below show four countries where the second wave has peaked and is coming down. Australia is somewhat unique in that its second wave peaked considerably higher than the first. Croatia and likely Spain will join that club.

The next two plots show 8 European countries in which a second wave has started and average new cases per day are growing. I have calculated average growth rates per day for the last 14 days and from that estimated Reff, the effective reproduction rate of the virus: the average number of secondary infections resulting from a single infection. Values over 1.0 mean the number of new cases will grow over time, values under 1.0 mean that new cases per day will decline. I calculated Reff using a simple approximate method [1], with an average serial interval between successive infections assumed to be 4.8 days [2,3].

New cases are growing in Switzerland, but at a relatively slow rate with Reff = 1.12. The current new case rate is one quarter of that at the peak of the first wave, and if new cases continue to grow at the same rate, Switzerland will reach the same level as the peak of the first wave in 55 days. With children having just gone back to school, its possible the effective reproduction rate will increase. Perhaps more alarmingly, the Reff is substantially higher in all four countries neighboring Switzerland: France, Germany, Austria and Italy. The UK has imposed mandatory quarantine for travellers from Switzerland, who join those from France and Spain. The UK has the slowest growth rate of the countries in this group (among those I have looked at) and Croatia the highest, having already substantially exceeded its first wave peak more than threefold.

The last figure shows four countries who have had an extended first wave, now declining, and may or may not yet have a second wave. It is no coincidence that three of the four countries in this category  – Brazil, Russia and the USA – are led by far-right nationalists who use technology as a tool for disinformation, demonize minorities and ignore climate change.  Sweden was one of the few European countries not to impose a compulsory lockdown and has had a much more extended epidemic as a result. It did ban gatherings of more than 50 people, but other measures were voluntary. Though I saw a post from a Swedish man recently, saying he was having a lot of trouble coping with the social distancing of 2 metres and asking how soon he could go back to his usual social distance of 5 metres.

I haven’t classified the USA as having two waves, because the first small plateau resulted from the peaking and decline of the epidemic in New York largely, while transmission continued to increase rapidly elsewhere, particularly in the South. I read an article today that described the USA as suffering from twin pandemics: covid-19 and stupidity.

Russia’s numbers are likely considerably under-reported. And all of these plots are for cases identified by testing. Trends may be affected by changes in testing rates, particularly for the earlier period of the first wave. And actual numbers of infections in the population are almost certainly much higher, likely by factors around 10-fold (it is 9-fold in Geneva).

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1 Response to The second wave of the Covid-19 pandemic

  1. Pingback: The twin pandemics and the second wave | Mountains and rivers

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