Intra-Country Spread of COVID and the role of Lockdowns
In a previous blog we examined the progress made against COVID in the four large democratic countries India, USA, Japan, and UK. We had examined the progress thru the prism of W0, an index we have developed to track phases of virus transmission (expansionary or in recession) and to identify, and highlight, the magnitude of W0. Like R0, the index used by epidemiologists to evaluate virus transmission, W0 also has the property that when it is greater than unity, it is indicative of the virus in expansion; when less than one, and persistently less than one, it is indicative of the beginning of the end of the virus. We have modelled the pattern of diffusion of the virus for every country the virus is present.
In this blog we analyze the progress of the five largest countries in Western Europe by population plus Belgium and Sweden. Table 1 summarizes the pace of transmission in Italy, France, Germany, Spain, Netherlands, Belgium, and Sweden, in terms of the latest value of W0 for each country and the value of the index 7, 14, 21 and 28 days earlier. This puts the current index into perspective, so we can judge whether the current value is part of a trend, or merely a spike or temporary occurrence. All five countries have gone below one, the critical threshold of transmission.
Just four weeks ago, on 26th March, all seven countries had a W0 of 1 or higher. A week later one country, Italy had moved rapidly downwards. Italy had gone through an explosive phase earlier, with the number of COVID cases tripling in one week — from 10149 on March 10 to 31506 Match 17th. Over the next week, perhaps because of the lockdown, cases slowed and by March 28th, W0 had gone below 1 and continued to decline rapidly over the next 21 days.