Coronavirus vs. Flu: Which Virus Is Deadlier?

The two maladies are similar in many ways, but people have more protection against seasonal flu

A discharged Covid-19 patient in Wuhan, China, bowed to the doctors while leaving the hospital on Tuesday.

PHOTO: STRINGER/GETTY IMAGES

By Betsy McKay

Updated March 10, 2020 12:49 pm ET

• PRINT
• TEXT
• 163

The new coronavirus and the seasonal flu are similar in many ways. Both are respiratory diseases that spread through droplets of fluid from the mouth and nose of someone who is infected. Both are contagious, produce similar symptoms and can be deadly.

But there are some major differences. While both produce many of the same symptoms—fever, cough and muscle aches—and are particularly hard on the elderly, they come from two different families of viruses. People have more protection from the flu because there is a vaccine and they are exposed to flu viruses every year.

There is no vaccine yet to protect people against Covid-19, the disease caused by the new virus.

“I think what we’re seeing with Covid-19 is what influenza would look like without a vaccine,” said Neil Fishman, who is chief medical officer at the Hospital of the University of Pennsylvania and an infectious-disease specialist.

RELATED

• This Common Flu Virus Is a Growing Threat
• The Deadly Flu No One Saw Coming
• Coronavirus Symptoms Start About Five Days After Infection, New Research Finds
• Japan Sees Silver Lining to Coronavirus as Flu Cases Drop

Scientists haven’t yet established exactly how deadly or transmissible the new virus is. But so far the new coronavirus appears to be deadlier than the seasonal flu, which kills thousands of Americans every season.

Calculations of the mortality rate for Covid-19 have ranged between 2% and 3.4% since the virus was identified in China in January, according to World Health Organization data. Those percentages are derived by dividing the number of confirmed deaths globally into the number of confirmed cases.

By contrast, the seasonal flu has a death rate of approximately 0.1%.

Covid-19’s higher death rate is one reason that billionaire global-health philanthropist Bill Gates recently warned in an article in the New England Journal of Medicine that “Covid-19 has started behaving a lot like the once-in-a-century pathogen we’ve been worried about.”

But public-health scientists say the real death rate is probably lower than the current estimates. U.S. health officials suggested in another article in the New England Journal of Medicine that the death rate could be well below 1%. (Other estimates have ranged between 1% and 2%.) That’s because current calculations are based on tallies of people who were ill enough to be tested, they wrote.

Coronavirus Outbreak Tests New Vaccine Development Strategy

YOU MAY ALSO LIKE

UP NEXT

0:00 / 4:18

Coronavirus Outbreak Tests New Vaccine Development Strategy

Scientists racing to find a vaccine for the Wuhan coronavirus are hoping a cutting-edge approach called “rapid response platforms” will quickly yield a breakthrough. WSJ’s Jason Bellini explains what these are and how they work. Photo: Tolga Akmen / AFP

Epidemiologists say they are certain there are many more people who were infected but didn’t receive a test—either because they weren’t ill enough to get one or didn’t have access to a test. Problems with a test developed in the U.S. means many people haven’t been able to get one.

Studies suggest there are also people who were infected but had no symptoms.

“We don’t know the proportion of mild or asymptomatic cases,” Marc Lipsitch, professor of epidemiology at Harvard T.H. Chan School of Public Health and director of the Center for Communicable Disease Dynamics, said in a recent teleconference.

In addition, the mortality rate has differed by region and by intensity of transmission, according to a report by an international mission to China of experts led by the WHO. It was 5.8% in an explosive initial outbreak in Wuhan. But in other, less-hard-hit areas of China, which had more time to prepare to care for patients, it was 0.7%. The rate in China has come down over time, the report said. In South Korea, which has had more than 7,000 cases, the mortality rate is 0.7%.

To calculate the “infection fatality rate”—meaning an infected person’s risk of death—will require large-scale studies to determine how many people in an area where there has been an outbreak have antibodies to the virus in their blood, Dr. Lipsitch said. That would show how many people had been infected, he said.

SHARE YOUR THOUGHTS

Have you been tested for flu or coronavirus? What was your experience? Join the conversation below.

Two blood tests have been licensed in China to conduct such studies, according to the WHO.

The new coronavirus, called SARS CoV-2, infects the lower respiratory tract. About 80% of people in a cohort of nearly 56,000 people in China had either mild or moderate illnesses, according to the report by the experts who traveled to China. Those illnesses started with a fever, dry cough, fatigue and other flulike symptoms, but sometimes included shortness of breath and progressed to a mild form of pneumonia, according to the report.

Another 13.8% became severely ill, requiring oxygen, and 6.1% were critical, meaning respiratory and organ failure, according to the report. People over the age of 60 and those with underlying conditions such as cardiovascular disease, chronic lung disease, diabetes and cancer were at highest risk, the report said.

Newsletter Sign-up

There are contradictory reports of how transmissible Covid-19 is. The disease does not seem to spread as easily as the flu, according to the WHO, which found that most of the spread in China was through close contacts like family members. Other disease modeling suggests the new virus is more transmissible than the flu.

Experts say the new coronavirus may appear to be more transmissible than flu right now because people have at least some immunity to seasonal flu viruses, since the flu goes around every year, and there is a flu vaccine.

About 34 million people in the U.S. have had the flu this season, which is still ongoing but starting to ease, according to the latest flu report from the Centers for Disease Control and Prevention. Of them, about 20,000 have died.

Flu strains change slightly every year, and the number of deaths depends on how severe the strains that are circulating that season are, according to the CDC. The most severe flu pandemic in recent history killed tens of millions of people in 1918 and 1919, meaning more than 2.5% of those it infected, according to CDC research.