A new National Bureau of Economic Research (NBER) working paper by Andrew Atkeson, Karen Kopecky, and Tao Zha focused on countries and U.S. states with more than 1,000 COVID deaths as of late July. In all, the study included 25 U.S. states and 23 countries.
Based on their analysis, the authors present four “Stylized Facts” about COVID-19, which are:
- Once a region reaches 25 total COVID deaths, within a month the growth rate in deaths per day falls to approximately zero. In other words, no matter the country or state and its policies, deaths per day stop increasing within 20-30 days of passing a threshold of 25 deaths.
- Once that happens, deaths per day either begin to fall or the trend remains flat.
- The variability in death trends across regions has fallen sharply since the beginning of the epidemic and remains low. All states studied, all countries studied, have become more similar in their trends and have remained so.
- Observations 1-3 suggest that the effective reproduction number, R, has hovered around one worldwide after the first 30 days of the epidemic.
The paper’s conclusion is that the data trends observed above likely indicate that nonpharmaceutical interventions (NPIs) – such as lockdowns, closures, travel restrictions, stay-home orders, event bans, quarantines, curfews, and mask mandates – do not seem to affect virus transmission rates overall.
Why? Because those policies have varied in their timing and implementation across countries and states, but the trends in outcomes do not.
From the study’s authors:
Location and sampling uncertainty. The black solid line in both charts represents the median posterior estimate. The solid magenta line in the top chart represents the median growth rate of 7-day smoothed daily deaths for all 50 locations and corresponds only to the left scale. The two dash-dotted bands in both charts contain two thirds of the posterior probability at each point in time and the two dashed bands, 0.90 of the posterior probability. The growth rates of death is estimated according to the fitted Weibull function. Effective reproduction numbers and normalized transmission rates are based on the SIR model. Day 0 is the earliest date when the cumulative death toll reached 25 in each location.