A firm estimate could help governments predict how many deaths would ensue if the virus spread out of control. The figure, usually called the infection fatality rate, could tell health officials what to expect as the pandemic spreads in densely populated nations like Brazil, India and Nigeria.
In poorer countries, the number could help officials decide whether to spend more on oxygen concentrators and ventilators, or on measles shots and mosquito nets.
At present, countries have very different case fatality rates, which measure deaths among patients known to have had Covid-19. In most cases, that number is highest in countries that have had the virus the longest.
According to data gathered by The New York Times, China had reported 90,294 cases as of Friday and 4,634 deaths, a case fatality rate of 5 percent. The United States, which has had a record number of new daily cases six times in the past two weeks, has had 2,811,447 cases and 129,403 deaths, about 4.6 percent.
Ten sizable countries, most in Western Europe, have tested bigger percentages of their populations than the United States has. Their case fatality rates vary wildly: Iceland’s is less than 1 percent, New Zealand’s and Israel’s are below 2 percent. Belgium, by comparison, is at 16 percent, and Italy and Britain are at 14 percent.
Before last week, the World Health Organization had no official estimate for the infection fatality rate. Instead, it had relied on a mix of data sent in by member countries and academic groups, and on a meta-analysis done in May by scientists at the University of Wollongong and James Cook University in Australia.
Those researchers looked at 267 studies in more than a dozen countries and then chose the 25 they considered the most accurate, weighting them for accuracy, and averaged the data. They concluded that the global infection fatality rate was 0.64 percent.