More Americans Are Surviving Covid-19
By Sarah Toy
The death rate from Covid-19 is falling in the U.S., according to infectious-disease experts and biostatisticians, a signal of advancements in treatment of the disease.
But the death rate could climb with the latest nationwide rise in cases, they warn.
The coronavirus is now killing around 0.6% of people it infects, an improvement from April, when the death rate was about 0.9%, says the Institute for Health Metrics and Evaluation at the University of Washington.
Jeffrey Shaman, an infectious-disease modeler at Columbia University’s Mailman School of Public Health, says the current death rate could be even lower than that, at roughly 0.15%. The death rate of seasonal influenza is 0.1%, based on data from the U.S. Centers for Disease Control and Prevention.
Death rates are also improving as infections shift toward younger people, who are at less risk of severe Covid-19 than older people, public-health experts say.
Controlling for factors like age and pre-existing illness, IHME director Christopher Murray says he and his colleagues found the drop in the national death rate can be largely linked to improvements in patient management and treatment. Doctors now have a better understanding of how to approach the respiratory issues caused by the virus, eschewing mechanical ventilation, which carries risks, in favor of less invasive methods of oxygenation. Routine use of anticlotting drugs and the steroid dexamethasone has also likely helped tamp down infection fatality rates in the U.S. overall, Dr. Murray says.
Researchers have labored over the past year to pin down the virus’s death rate, which helps public-health experts and authorities project the course and severity of the pandemic. Since the beginning of the pandemic, health authorities have tracked a metric known as the “case fatality rate,” the number of deaths divided by all recorded cases of Covid-19, but epidemiologists say that metric doesn’t accurately reflect the true death rate because it doesn’t count people who don’t get tested.
That was especially true early on in the pandemic, when testing wasn’t widely available. Scientists also know now that many people don’t have symptoms when they get infected, and asymptomatic people often don’t seek out testing. Both issues have led to case fatality rates that are higher than the actual death rate, though the two are beginning to converge as testing becomes more widely available, epidemiologists say.
In contrast, the so-called “infection fatality rate” measures the number of deaths as a fraction of all Covid-19 infections, regardless of symptoms or testing status. Researchers all have slightly different ways of calculating the infection fatality rate, but most use complex mathematical models and surveys of blood tests that identify people in a population who have antibodies against the coronavirus. That helps them identify what’s known as the ascertainment rate, an estimate of the number of confirmed cases as a fraction of actual infections. Researchers can then estimate the total number of people infected within a period and use that to gauge the true death rate.
The recent improvement could prove short-lived if cases in the U.S. continue to surge, public-health experts say, although they haven’t modeled exactly what that could look like. Death rates will likely climb again as patients overwhelm hospitals, straining their capacity and staff and lowering quality of care, they say. The U.S. has now topped 12.4 million confirmed cases, and hospitalizations have hit several record highs.
“When cases go up, as they are here and in Europe, hospitals get overcrowded and death rates rise,” said Florian Krammer, a professor of vaccinology at the Icahn School of Medicine at Mount Sinai.
Death rates can change depending on the availability of health-care resources, such as hospital beds and staffing in an area. That, along with the location’s patient demographics, explains why rates vary from place to place, he and other experts say.
States and municipalities that have the virus under control and aren’t overwhelmed will tend to have lower death rates, said Dr. Krammer, who recently published a paper in Nature estimating the infection fatality rate of Covid-19 in the spring in New York City, which he and his colleagues pegged at around 1%. The death rate can swing between around 0.2% and 1.5% depending on the location, he noted.
“It’s dynamic,” he said.
The metric is also extremely sensitive to the age of patients, as well as their pre-existing health problems, public-health experts and biostatisticians say. People who are older are more likely to die of Covid-19, as are people who struggle with obesity, diabetes or other issues that increase the risk of having a severe course of illness.
When IHME researchers estimated the death rates in each state in early November, the metric ranged from place to place. In Florida it was 0.7%, while in Alaska it was 0.4%. IHME said it didn’t take into account case loads or health-care system capacity for these calculations, and the different rates among states were mostly due to the age of those in the population and rates of obesity.