So far, the new coronavirus has led to more than 89,000 illnesses and 3,000 deaths worldwide. But that's nothing compared with the flu, also called influenza. In the U.S. alone, the flu has caused an estimated 32 million illnesses, 310,000 hospitalizations and 18,000 deaths this season, according to the Centers for Disease Control and Prevention (CDC).
That said, scientists have studied seasonal flu for decades. So, despite the danger of it, we know a lot about flu viruses and what to expect each season. In contrast, very little is known about the new coronavirus and the disease it causes, dubbed COVID-19, because it's so new. This means COVID-19 is something of a wild card in terms of how far it will spread and how many deaths it will cause.
"Despite the morbidity and mortality with influenza, there's a certainty … of seasonal flu," Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said in a White House press conference on Jan. 31. "I can tell you all, guaranteed, that as we get into March and April, the flu cases are going to go down. You could predict pretty accurately what the range of the mortality is and the hospitalizations [will be]," Fauci said. "The issue now with [COVID-19] is that there's a lot of unknowns."
Scientists are racing to find out more about COVID-19, and our understanding of the virus that causes it and the threat it poses may change as new information becomes available. Based on what we know so far, here's how it compares with the flu.
Symptoms and severity
Both seasonal flu viruses (which include influenza A and influenza B viruses) and COVID-19 are contagious viruses that cause respiratory illness.
Typical flu symptoms include fever, cough, sore throat, muscle aches, headaches, runny or stuffy nose, fatigue and, sometimes, vomiting and diarrhea, according to the CDC. Flu symptoms often come on suddenly. Most people who get the flu will recover in less than two weeks. But in some people, the flu causes complications, including pneumonia. So far this flu season, about 1% of people in the United States have developed symptoms severe enough to be hospitalized, which is similar to the rate last season, according to data from the CDC.
With COVID-19, doctors are still trying to understand the full picture of disease symptoms and severity. Reported symptoms in patients have varied from mild to severe, and can include fever, cough and shortness of breath, according to the CDC.
In general, studies of hospitalized patients have found that about 83% to 98% of patients develop a fever, 76% to 82% develop a dry cough and 11% to 44% develop fatigue or muscle aches, according to a review study on COVID-19 published Feb. 28 in the journal JAMA. Other symptoms, including headache, sore throat, abdominal pain, and diarrhea, have been reported, but are less common.
Another recent study, considered the largest on COVID-19 cases to date, researchers from the Chinese Center for Disease Control and Protection, analyzed 44,672 confirmed cases in China between Dec. 31, 09 and Feb. 11, 2020. Of those cases, 80.9% (or 36,160 cases) were considered mild, 13.8% (6,168 cases) severe and 4.7% (2,087) critical. "Critical cases were those that exhibited respiratory failure, septic shock, and/or multiple organ dysfunction/failure," the researchers wrote in the paper published in China CDC Weekly.
It's important to note that, because respiratory viruses cause similar symptoms, it can be difficult to distinguish different respiratory viruses based on symptoms alone, according to WHO.
Death rate
The death rate from seasonal flu is typically around 0.1% in the U.S., according to The New York Times.
The death rate for COVID-19 appears to be higher than that of the flu.
In the study published Feb. 18 in the China CDC Weekly, researchers found a death rate from COVID-19 to be around 2.3% in mainland China. Another study of about 1,100 hospitalized patients in China, published Feb. 28 in the New England Journal of Medicine, found that the overall death rate was slightly lower, around 1.4%.
Still, the death rate for COVID-19 appears to vary by location and an individual's age, among other factors. For instance, in Hubei Province, the epicenter of the outbreak, the death rate reached 2.9%; in other provinces of China, that rate was just 0.4%, according to the China CDC Weekly study. In addition, older adults have been hit the hardest. The death rate soars to 14.8% in those 80 and older; among those ages 70 to 79, the COVID-19 death rate in China seems to be about 8%; it’s 3.6% for those ages 60 to 69; 1.3% for 50 to 59; 0.4% for the age group 40 to 49; and just 0.2% for people ages 10 to 39. No deaths in children under 9 have been reported.
Virus transmission
The measure scientists use to determine how easily a virus spreads is known as the "basic reproduction number," or R0 (pronounced R-nought). This is an estimate of the average number of people who catch the virus from a single infected person, Live science previously reported. The flu has an R0 value of about 1.3, according to The New York Times.
Researchers are still working to determine the R0 for COVID-19. Preliminary studies have estimated an R0 value for the new coronavirus to be between 2 and 3, according to the JAMA review study published Feb. 28. This means each infected person has spread the virus to an average of 2 to 3 people.
It's important to note that R0 is not necessarily a constant number. Estimates can vary by location, depending on such factors as how often people come into contact with each other and the efforts taken to reduce viral spread, Live Science previously reported.
Risk of infection
The CDC estimates that, on average, about 8% of the U.S. population gets sick with the flu each season.
As of March 2, there are 91 cases of COVID-19 in the U.S., including 43 detected through public health surveillance and 48 among Americans who were "repatriated" to the U.S. Still, newly emerged viruses like this one are always of public health concern, according to the CDC. It's unclear how the situation with this virus in the U.S. will unfold, the agency said. Some people, such as health care workers, are at increased risk for exposure to COVID-19.
Pandemics
It's important to note that seasonal flu, which causes outbreaks every year, should not be confused with pandemic flu, or a global outbreak of a new flu virus that is very different from the strains that typically circulate. This happened in 2009 with the swine flu pandemic, which is estimated to have killed between 151,000 and 575,000 people worldwide, according to the CDC. There is no flu pandemic happening currently.
The COVID-19 outbreak has not yet been declared a pandemic. But on Jan. 30, the WHO declared the COVID-19 outbreak a "public health emergency of international concern." The declaration was primarily due to concern that the virus could spread to countries with weaker health systems.