As of March 31, Vollmer and Bommer calculate, confirmed cases represented just 3.5 percent of infections in Italy, 2.6 percent in France, 1.7 percent in Spain, 1.6 percent in the United States, and 1.2 percent in the U.K. In other words, the true number of infections was between 29 and 83 times as high as the official tallies in those countries. The countries with the highest estimated detection rates were South Korea (nearly 50 percent), Norway (38 percent), Japan (25 percent), and Germany (16 percent). With the exception of Japan, all of those countries have tested a relatively large percentage of their populations. The estimated prevalence of infection ranged from 0.1 percent in India and Japan to more than 13 percent in Turkey; it was 3.6 percent in the United States.

“The average detection rate is around six percent, making the number of cases that is reported in the news on a daily basis rather meaningless,” Vollmer and Bommer conclude. Vollmer adds: “These results mean that governments and policy makers need to exercise extreme caution when interpreting case numbers for planning purposes. Such extreme differences in the amount and quality of testing carried out in different countries mean that official case records are largely uninformative and do not provide helpful information.” Bommer notes that “major improvements in the ability of countries to detect new infections and contain the virus are urgently needed.”