A jogger wears a mask adjacent to the beach in La Jolla. Photo by Chris Stone

By Dr. Hai Shao

In the midst of dealing with a pandemic, it’s hard to believe that the flu season will soon be upon us. This realization leaves some worrying that the two 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 Centers for Disease Control and Prevention report that COVID-19 is proving to be more deadly than the seasonal flu — especially for older adults and people with underlying health condition — 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 Infection

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, it is plausible to suspect that people can be infected by both at the same time.

Even more concerning 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, 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.

The Upside of Flu Season During a Pandemic

The good news is that the precautions we have been taking for several months to decrease the spread of COVID-19 — hand-washing, wearing face coverings and social distancing — 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.

Current public health measures would significantly decrease the risk of viral transmission for other common cold viruses as well as influenza. It is widely predicted that if people are following guidance of public safety for COVID-19 prevention, we could have a much milder season for influenza this year.

In addition to preventive steps to slow transmission of both illnesses, the flu vaccine and vaccination against COVID-19 — when available — will be pivotal to achieve herd immunity and significantly decrease both infections in the community. I encourage people aged 6 months and older to get the flu vaccine as directed by their health care providers. And once a scientifically proven, safe and effective vaccine for COVID-19 is available, we should get vaccinated as soon as possible.

Dr. Hai Shao is a board-certified infectious disease specialist affiliated with Sharp Chula Vista Medical Center.