• Leon Grice

United States gets Reff under control

Since 26 July 2020, and for nearly three weeks, the United States has suppressed COVID-19 below reproduction 1.0. That means the States' physical distancing, testing and tracing policies are controlling the pandemic and the number of total new cases will reduce. It feels bad at the moment because active cases are still relatively high and fatalities are increasing, but we, in the CloseAssociate team, can confidently predict that the US is on track to getting daily new cases down in the next couple of weeks (all things staying the same). In contrast, many European States do not look good (but that's for another blog post).

The States: Arizona, Florida, Texas and California who had steep increases in new daily cases in June are now well under control and Reff < 1.0 now for each State, albeit with hotspot counties. California's Alameda Country has Reff > 2.9 which is cause for concern, even though daily case data from John Hopkins is patchy. Northern California is now not doing as well as Southern California. (explore covid19.closeassociate.com to look closely at each US county).


A feature of COVID-19 is the lag time between infection and onset of symptoms, and a lag time between first symptoms and recovery or death. Not to mention the pesky feature that many infected people are asymptomatic and these people and those yet to display symptoms can shed the virus and infect others. One of the key advantages of our new SIR+B method is it provides a 10-14 day heads up on the amount and direction of new daily cases. There is no other method that gives as accurate or as early warning which given COVID-19's unique features is a of significant value for public health decision-making.

But there are some problems in the United States. North Dakota, South Dakota, Nebraska, Massachusetts and New Jersey have worrying trends and Reff values persistently above 1.0. The worry is these north eastern States could put pressure on New York which had a very tough time in late summer and spring. And many States have an "Alameda" and the CloseAssociate team's advice for US Governors and Mayors is to focus on your hotspot counties with suppression policies to get Reff < 1.0.

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