It depends on what you mean by "worse"...

By Leah Groth
February 26, 2020

Each year, from around October through May, international health coverage is primarily focused on the flu—and with good reason: The flu is notoriously infectious and can cause up to 45 million illnesses each year, according to the Centers for Disease Control and Prevention. But this year, the new coronavirus outbreak (aka, COVID-19) is dominating the headlines, causing more than 80,000 illnesses in just over two months.

Both viruses—influenza and coronavirus—are highly infectious diseases with similar symptoms, transmission, and prevention methods, but is one necessarily worse than the other? Here, infectious disease experts across the US compare all aspects of both illnesses, to determine whether coronavirus is any worse than the flu—or vice-versa.

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Both seasonal flu viruses (which include influenza A and influenza B viruses) and COVID-19 are contagious viruses that cause respiratory illness. 

According to the CDC, the flu typically manifests itself in symptoms such as fever, cough, sore throat, muscle aches, headaches, runny or stuffy nose, fatigue and, occasionally, vomiting and diarrhea—typically, the latter two are more common in children. Those flu symptoms often come on suddenly after an incubation period of two to five days. 

While the majority of people infected with the flu will be fully recovered in about two weeks, for some people (most often those with compromised immune systems), the flu can lead to complications like pneumonia. According to recent data from the CDC, this year just 1% of people suffering from the flu have been hospitalized.

As for COVID-19, researchers are still scrambling to compile thorough and accurate data to understand how the disease works. One study, involving just 100 people with the virus, published Jan. 30 in the journal The Lancet, noted that the most common symptoms were fever, cough and shortness of breath, with approximately 5% reporting sore throat and runny nose, and just 1-2% reporting diarrhea, nausea and vomiting. Those symptoms, however, usually come on a bit more gradually after an incubation period of two to 14 days. 

If they sound extremely similar, that's because they are, according to Manisha Juthani, MD, a Yale Medicine infectious disease specialist. “Based on symptoms alone, COVID-19 and flu are very difficult to distinguish,” says Dr. Juthani.

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Treatment, vaccines, and prevention

The first and most major difference between the flu and novel coronavirus, is how little we know about the latter—which plays into into the absence of treatment and vaccines for COVID-19. "People often compare the flu to COVID-19, but we have a vaccine to prevent and medications to treat the flu. Right now, we have no medications or vaccine for COVID-19," says Dr. Juthani.

The influenza vaccine, for example, was first licensed for use in civilians in 1945—and now, doctors recommend all people over six months old get the flu shot each year, ideally as early as the end of October. Treatment for the flu is also an option, with antiviral medications like Tamiflu, which can shorten the amount of time you're sick and prevent flu complications like pneumonia. But, for Tamiflu to work effectively, it needs to be taken with in the first 48 hours of the onset of symptoms—and most flu cases are so mild they may not even need treatment other than rest and symptom management.

While scientists are currently working on a coronavirus vaccine, it likely won't be ready in time to combat the current outbreak, Jeremy Brown, MD, director of the Office of Emergency Care Research at the National Institutes of Health and author of Influenza: The Hundred-Year Hunt to Cure the Deadliest Disease in History, previously told Health. That's because the entire vaccine process—from early development through human testing—can take a lot of time and cost a lot of money. Fortunately, in working on a vaccine for the current coronavirus, researchers may discover clues that may help treat or even prevent future outbreaks.

At this point, the best options for keeping yourself infection-free is following the CDC’s recommendations for all respiratory illnesses. That includes washing your hands often with soap and water for at least 20 seconds; not touching your eyes, nose and mouth with unwashed hands; avoiding close contact with people who are sick; staying home when you are sick; and disinfecting frequently touched objects and surfaces.

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Virus transmission

Researchers still aren't sure how contagious COVID-19 is compared to other viruses, but it appears to spread more rapidly than the flu. “In public health we measure something called the R0 (pronounced 'R-naught') which is the average number of people infected by a person with the virus,” says Dr Brown. He goes on to explain that the R0 for influenza is about 1.3, meaning about 1.3 people get the virus from every ten who have the infection. Measles, on the other hand, is extremely contagious, with an R0 of 12-18. “We are still not sure what the R0 is for coronavirus, but it appears to be about 2.0, which is about the same as SARS,” Dr. Brown continues. “These are early estimates though and are likely to change as we get better data.”

In both the flu and coronavirus, however, the main method of transmission appears to be from person to person via respiratory transmission—essentially by coming in close contact (within six feet) with respiratory droplets from the coughs and sneezes of infected people. The flu and coronavirus also have similar periods of time when people are asymptomatic but still contagious. “It appears that with both viruses, people may be able to transmit the virus before they are symptomatic,” explains Dr. Juthani. 

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Severity of infections and death rate

Most people who contract the flu will recover in a few days to less than two weeks, per the CDC—but a small number of people may develop complication, some of which can be life-threatening. People at a higher risk for these complications include those over 65, anyone who has a chronic medical condition, pregnant women, and children under 5 years old.

Globally, the World Health Organization (WHO) estimates that the flu kills 290,000 to 650,000 people each year, and per the CDC, up to 61,000 of those deaths occurred in the US annually since 2010.

While we don't have yearly estimates for coronavirus fatalities yet, the WHO's newest Situation Report, published on February 25, says that out of the 80,239 confirmed coronavirus cases worldwide, the illness has resulted in 2,700 deaths—2,666 of which have occurred in China.

It's also important to note that a recent investigation by the Chinese Center for Disease Control and Protection, published in JAMA, analyzed data compiled between Dec. 31, 09 and Feb. 11, 2020 of 44,672 confirmed cases in China—80% of which were considered mild, and only 4.7% were critical.

Overall, per the CDC, the death rate of those who have been infected with the flu this flu season is 0.05%. According to the research conducted by the Chinese CDC, the case-fatality rate of novel coronavirus in China is 2.3%. 

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So overall, which is worse: coronavirus or flu?

That's not really an easy question to answer, says Dr. Brown. "It depends on what you mean by worse,” he says. “More easily spread? Then it appears to be coronavirus. Causes more cases of serious illness. Then it’s flu.”

Another thing that makes the coronavirus a bit more dangerous? That there are so many unknowns attached to it—unlike the flu which has been studied for decades. "Despite the morbidity and mortality with influenza, there's a certainty … of seasonal flu. 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]," Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said in a White House press conference on Jan. 31. "The issue now with [COVID-19] is that there's a lot of unknowns." 

Either way, with new cases of COVID-19 being identified in Iran, Italy, and South Korea, Dr. Juthani believes we should be prepared for community spread of COVID-19 in the United States. “Until a vaccine is developed or pharmaceutical agents are identified that can treat COVID-19, we will need to use the same tactics we are familiar with for preventing flu to prevent COVID-19,” she says.   

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.

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