The World Health Organization on Tuesday stated that the global case fatality rate is 3.4 percent. But that figure can be misleading if not framed correctly, and the official case fatality rate is likely to drop in coming months.
U.S. health officials on Thursday briefed lawmakers in Congress and said they believe the case fatality rate in this country will most likely be in the range of 0.1 to 1.0 percent, meaning somewhere between one of every thousand and one of every hundred people with covid-19 will die.
That would make covid-19 closer in lethality to influenza in severe or pandemic flu seasons, according to an article in the New England Journal of Medicine co-authored by Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. The article states that the true fatality rate of covid-19 “may be considerably less” than 1 percent, and “may ultimately be more akin to those of a severe seasonal influenza (which has a case fatality rate of approximately 0.1%) or a pandemic influenza (similar to those in 1957 and 1968) rather than a disease similar to SARS or MERS, which have had case fatality rates of 9 to 10% and 36%, respectively.”
The WHO’s fatality percentage, announced Tuesday, is based simply on the number of deaths globally (the numerator) and the number of confirmed cases of covid-19 (the denominator). As of Friday the WHO had counted 3,400 deaths among 100,000 cases.
But the official numbers do not capture the full scope of the contagion. The actual number of deaths from the virus might be somewhat higher, in part because of undercounting or misdiagnosis. There is little doubt that the number of infections — in many cases among people who either did not get sick or thought they had only a mild illness — is larger than the official case count. The infection rate will not be known until researchers do broad surveys to see who has developed antibodies to the virus.
“Many people don’t get sick and don’t get tested,” Brett P. Giroir, assistant secretary for health at the U.S. Department of Health and Human Services, told reporters Thursday after participating in a closed-door briefing for House members.
“The modeling suggests that we have a denominator problem. If you’re really sick and you have respiratory failure, you go see someone and you get tested. But if you’re not very ill, as most people are not, they do not get tested. They do not get counted in the denominator, especially in a crisis situation like in China,” he said.
As late as Friday afternoon, the United States had 14 deaths among 260 cases, a rate of 5.4 percent. But testing has been slow in the U.S., and as it becomes more widespread the rate will plummet.
“Your denominator is going to explode, which will push the case fatality rate down. But it will also push the number of affected persons and communities up,” said Kathleen Jordan, vice president and chief medical officer of Saint Francis Memorial Hospital in San Francisco.
The enigmatic nature of the new virus and the many unknowns about its trajectory have put people on edge, she said.
“I do think people tend to panic when it’s unknown. Just having information about how it spread, how to protect yourself, it calms people down and makes them act appropriately and effectively,” she said.
A report from 25 researchers from China, the United States and six other countries and published by the WHO suggests the current high fatality rate is skewed by the terrible death toll in the first chaotic weeks of the outbreak in Wuhan, China. People who became sick in the first 10 days of January experienced a 17.3 percent death rate, the report said.
But among people developing symptoms after Feb. 1, the fatality rate has been 0.7 percent, the report said, noting that “the standard of care has evolved over the course of the outbreak.”
The first cases in Wuhan were identified at the end of December. Not until Jan. 23 did the Chinese authorities impose severe travel restrictions designed to contain the spread of the coronavirus, officially known as SARS-CoV-2.
In those early days, doctors struggled to understand what they were dealing with and how best to treat patients, and “were quite overwhelmed,” said Christine Kreuder Johnson, an epidemiologist at the University of California at Davis.
“That can create a high case fatality rate because you can only tackle the most severe cases,” she said. “You’ve got patients that might not get the same care they might get in other circumstances — in peacetime, as we say.”
Another new study from China, based on 1,099 patients in 552 hospitals across the country, put the case fatality rate there at 1.4 percent.
“At this point it’s all speculative. We don’t know the denominator,” said Columbia University epidemiologist Ian Lipkin, who recently visited China.
The China data does not necessarily predict what will happen elsewhere, said Michael Osterholm, an infectious disease expert at the University of Minnesota.
“You can’t just take Chinese data and suddenly lay it over the United States. And say it’s going to be 2 percent or 3,” he said. “It’s going to be totally a reflection of the at-risk population. What are the underlying risk factors? Obesity? Smoking? Over 60 percent of Americans have an underlying health problem that could contribute to a poor outcome with this event.”
China has a higher case fatality rate than South Korea, where, as of Thursday, 35 people had died among 6,088 cases — a rate of 0.57 percent. Germany has reported 262 cases but zero deaths.
A new study suggests the virus has split into two strains and a less aggressive strain is now more prevalent than a deadlier one. But that is a preliminary report and not confirmed.
The report said reviews of 103 samples of the virus showed two distinct strains, which the authors name the L and the S strains. They hypothesized that the more aggressive L strain sickened people to the point that they sought medical treatment or other interventions. That would have made it less likely to spread. A less aggressive strain, the S type, could have circulated more easily over time among people who continued about their daily lives.
Jeffery Taubenberger, a virologist at the National Institute of Allergy and Infectious Diseases, said he would have to see “a lot more convincing data before I would begin to think that hypothesis was supported.”
He said the study did not contain enough data showing a clear link between the different strains and different medical outcomes. But animal viruses do mutate soon after they enter a new species, such as human beings, he said: “Certain adaptations are necessary. It’s likely that change will occur early on in the pandemic.”
Taubenberger is an expert on influenza pandemics, including the 1918 Spanish Flu, the worst in history. Estimates of the fatality rate of Spanish Flu are impeded by a lack of data on how many people were infected. But Taubenberger said a plausible estimate is a 1.1 percent case fatality rate in the United States and 4.6 percent globally.
In 1957, the influenza pandemic probably had a U.S. fatality rate of about 0.07, he said.
Asked to appraise the current coronavirus epidemic, he said, “Right now, to me, it looks like it’s sort of on par with an influenza pandemic in its impact. Obviously we hope it’s not going to be a 1918-like impact. It’s something we definitely need to take seriously.”