For the media

Does the flu make you more susceptible to COVID-19?

By The Health News Team | December 1, 2023
Sick woman blowing her nose

Flu season is upon us — while COVID-19 and RSV still pose a risk. This realization leaves some worrying that respiratory illnesses could hit like a one-two punch, causing more — and possibly more severe — illness.

COVID-19 and the flu are similar in some ways, but are caused by different viruses. Both flu and COVID-19 are spread from person-to-person and can cause varying illness from mild to severe. They also share some symptoms, including:

  • Fever or feeling feverish/chills

  • Cough

  • Shortness of breath or difficulty breathing

  • Fatigue

  • Sore throat

  • Runny or stuffy nose

  • Muscle pain or body aches

  • Headache

  • Vomiting and diarrhea (more common in children than adults)

While the CDC reports that COVID-19 is more deadly than the seasonal flu, especially for older adults and people with underlying health conditions, the flu can be more dangerous for children. However, there is still much to be learned about COVID-19, including whether having the flu makes you more susceptible to being infected by the novel coronavirus that causes the disease, and whether having both at the same time might lead to more severe illness.

The risk of dual diagnosis

“Although there is no clinical evidence so far to suggest that one viral infection, such as influenza, increases susceptibility of being infected by another virus, such as the novel coronavirus that causes COVID-19, it is plausible to suspect that people can be infected by both at the same time,” says Dr. Hai Shao, a board-certified infectious disease specialist affiliated with Sharp Chula Vista Medical Center. “The cell tropism, which are the cells and tissues in your body that support growth of a particular virus or bacteria, and cell surface receptors that induce changes in cell activity are different for each virus.”

Even more concerning, according to Dr. Shao, is that both viruses target and damage the respiratory tract, primarily while stimulating a robust immune response. The risk of having more severe symptoms and severe complications caused by dual infection, such as acute respiratory distress syndrome (ARDS), multi-organ system failure, or sepsis and subsequent bacterial pneumonia, is conceivably higher.

Other common respiratory symptoms — nasal congestion, runny nose, sore throat and productive cough — might also be increased in severity. And the duration of the symptoms, both mild and severe, could be longer.

Preventing a severe flu season

The good news is that the precautions we have been taking to decrease the spread of COVID-19 can also decrease the risk of getting the flu. This is because both viruses spread and transmit via respiratory droplets when people who are infected breathe, speak, cough and sneeze. We should maintain these preventive measures, especially when feeling sick or around others who are sick.

“Thanks to nationwide public health measures we have had three very mild influenza seasons in a row,” Dr. Shao says. “With the same vigilance paired with vaccination, we can significantly decrease influenza and COVID-19 infections in the community for the next few months.”

According to Dr. Shao, people age 6 months and older should get both the flu and COVID-19 vaccines as directed by their health care providers. Additionally, COVID-19 boosters for eligible people age 5 and older are recommended.

Get flu and COVID-19 vaccine information and access to resources from Sharp.

For the news media: To speak with Dr. Shao for an upcoming story, please contact Erica Carlson at

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