Is COVID-19 Worse Than the Flu?

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 41 million illnesses each year, according to the Centers for Disease Control and Prevention (CDC). But since 2019, COVID-19 has shared the spotlight with the flu, causing millions to fall ill.

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.

Flu Symptoms

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/stuffy nose
• Fatigue
• Vomiting (more common in children)
• Diarrhea (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 the CDC.

COVID-19 Symptoms

As for COVID-19, the CDC describes a wide range of symptoms, such as:

• Fever
• Cough
• Shortness of breath
• Difficulty breathing
• Muscle pain
• Headache
• Diarrhea
• Nausea
• Sore throat
• Loss of taste or smell

These symptoms can occur between two to 14 days after exposure to the virus. One study, published in January 2020 in The Lancet, noted that the most common symptoms were fever, cough, and shortness of breath. This article from 2021 from UpToDate, states that roughly one-third of patients with COVID-19 experience gastrointestinal symptoms as well.

If the symptoms of the flu and COVID-19 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."

Flu Treatment, Vaccines, and Prevention

The influenza vaccine was first licensed for use in civilians in 1945, according to the CDC. Now, healthcare providers recommend all people over six months old get the flu shot each year, ideally around September and October, according to the CDC.

Treatment for the flu is also an option. There are antiviral medications like Tamiflu, which can shorten the amount of time you're sick and prevent flu complications like pneumonia, according to the CDC. In order for Tamiflu to work effectively, it needs to be taken within the first 48 hours of the onset of symptoms, according to the US Food & Drug Administration (FDA). Most flu cases are so mild they may not even need treatment other than rest and symptom management.

COVID-19 Treatment, Vaccines, and Prevention

The COVID-19 vaccines will protect individuals from serious illness, including hospitalization and death, according to the CDC. The first COVID-19 vaccine—the Pfizer-BioNTech vaccine—was authorized for emergency use in December 2020, according to the US Department of Health & Human Services.

In addition to vaccines, to keep yourself infection-free from COVID-19 you should follow the CDC's recommendations. That includes:

• Getting tested for COVID-19
• Avoiding close contact with people who are sick
• Staying home if you are sick
• Maintaining social distance
• Wearing a mask
• Moving indoor activities outdoors

Virus Transmission

In both the flu and COVID-19, 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, according to the CDC. The flu and COVID-19 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," explained Dr. Juthani.

"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," said 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.

Dr. Brown explained 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. (But, of course, we have a measles vaccine).

As for COVID-19? Varying data on the R0 for SARS-CoV-2 was released. There is a R0 of 5.7 based on data from China and published in July 2020 in Emerging Infectious Diseases. There is also a reported R0 of 1.4-2.4 based on data from the World Health Organization (WHO) which was published in this review in November 2020 in the Indian Journal of Critical Care Medicine.

According to the articles, if the R0 is lower, at a value of 2.2, then the percentage of the population needing to have either had the disease or the vaccination needs to be 55% in order to create herd immunity.

But, if the R0 is higher, at 5.7, this means that 82% of the population must be immune to the virus—through vaccination or prior infection—to achieve so-called herd immunity. Which, according to this article from March 2022 in The Journal of Infectious Diseases, herd immunity may not be possible for COVID-19 or influenza. This is because both viruses are constantly mutating and changing and vaccines or prior infections wouldn't protect against a new mutation.

Severity and Death Rate

COVID-19 and the flu can result in severe disease in older adults and those with underlying health conditions, according to the CDC. However, COVID-19 can cause more severe illnesses than the flu. It can also cause serious illness in people who are young and relatively healthy.

Globally, the WHO estimates that the flu kills 290,000 to 650,000 people each year. In contrast, from January 2020 to December 2021, there was an estimated 14.9 million deaths associated with COVID-19, according to the WHO. However, this tally did not separate those that died directly from COVID-19 from those that died indirectly from COVID-19. According to STAT, this number includes people who were unable to receive medical care due to the overburden of health systems as a result of the pandemic. The actual number of COVID-related deaths is closer to 1 million at the end of 2021.

Summary

There are quite a few similarities and differences between influenza and COVID-19. While both have similar symptoms and a vaccine for prevention, COVID-19 can be more severe and affect young and healthy people in addition to older adults and those with prior health conditions. Both viruses transmit from person to person via respiratory droplets. However, COVID-19 has been found to be more contagious.

At the end of the day, both viruses cause illness, some more severe than others. It is important to protect yourself against both viruses by making sure you are up to date on your vaccines.

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.