The number of COVID-19 deaths cannot be directly compared to the number of seasonal influenza deaths because they are calculated differently, researchers say in a report released today.
Whereas COVID-19 death rates are determined from actual counts of people who have died, seasonal influenza death rates are estimated by the Centers for Disease Control and Prevention (CDC) using population modeling algorithms, explains Jeremy Samuel Faust, MD, with Harvard Medical School and Brigham and Women’s Hospital, Division of Health Policy and Public Health in Boston, Massachusetts.
The CDC estimates that between 24,000 and 62,000 people died from influenza during the 2019-2020 season (through April 4). At the time of the analysis (as of April 28), COVID-19 deaths had reached 65,000 in the United States.
But making that comparison “is extremely dangerous,” Faust told Medscape Medical News.
“COVID-19 is far more dangerous and is wreaking far more havoc than seasonal influenza ever has,” he said.
Faust coauthored the perspective article, published online in JAMA Internal Medicine, with Carlos del Rio, MD, Division of Infectious Diseases at Emory University School of Medicine in Atlanta, Georgia.
The message and methodology of Faust’s and del Rio’s article are on target, according to Jonathan L. Temte, MD, PhD, who has been working in influenza surveillance for almost 25 years.
Current flu data draw on limited information from primary care practices and hospitals, said Dr. Temte, associate dean for public health and community engagement at the University of Wisconsin School of Medicine and Public Health in Madison. The estimates help bridge the gaps, he said, but the system is inherently vulnerable to error.
“Comparing them – as so many people in this country have done – to try to diminish the impact of SARS-CoV2 is not fair,” he said.
Estimated versus actual influenza deaths
The authors illustrate the difference in the way rates of death from influenza are calculated: “Between 2013-2014 and 2018-2019, the reported yearly estimated influenza deaths ranged from 23,000 to 61,000. Over that same time period, however, the number of counted influenza deaths was between 3,448 and 15,620 yearly.”
“It’s apparent [the CDC has] been overestimating,” Faust said. “If you publish a number on the higher end of the estimate, people might take your public health messages more seriously, such as, it’s important to get your yearly flu shot.”
He added that until influenza death rates started to be compared with COVID-19 rates, “there was never really a downside” to reporting estimates.
Dr. Temte said he doesn’t regard overestimating flu deaths as intentional but rather the result of a longstanding “bias against the elderly in this country” that the estimates are meant to account for.
For example, he says, reporting influenza deaths is mandatory when such deaths involve persons younger than 18 years but not when they involve adults.
Also, traditionally, influenza has been seen “as a cause of death in people with multiple comorbidities that was just part and parcel of wintertime,” Dr. Temte said.
“The likelihood of being tested for influenza goes down greatly when you’re older,” he said. “This is slowly changing.”
The CDC acknowledges on its website that it “does not know the exact number of people who have been sick and affected by influenza because influenza is not a reportable disease in most areas of the US.”
It adds that the burden is estimated through the US Influenza Surveillance System, which covers approximately 8.5% of the US population.