It’s a familiar rite of autumn: Neighborhood pharmacies hang their “Flu Shot Available Here” signs. Primary care providers fill our email inboxes with reminders to get our annual vaccinations.This year is different. We’re facing a “twindemic” of both the seasonal flu and COVID-19, and research shows it’s possible to get sick with both respiratory illnesses at the same time. Unfortunately, history proves people haven’t done a good job of taking the flu seriously enough. Just 45 percent of adults in the United States got the flu shot last year, according to the Centers for Disease Control and Prevention, even though the seasonal version of the disease is deadly, killing an average of 37,000 people every year over the past decade. Having both diseases in play simultaneously threatens to tax our health-care systems and puts lives at risk like never before. That’s not to mention the real possibility that a strain of bird flu lurking at poultry markets could jump to humans and cause an overlapping pandemic.National Geographic asked two infectious disease experts to weigh in on what’s at stake with this year’s dual threat, and why we all should get vaccinated against the flu as early as possible. The following interviews have been edited for length and clarity.Getting COVID-19 is significantly worse than the flu. So why are public health officials suddenly worried about flu shots?Lisa Maragakis, senior director of infection prevention at Johns Hopkins University School of Medicine in Baltimore, Maryland:The symptoms for flu and COVID-19 are so similar that one of the challenges we’re dealing with this year is diagnosing people correctly and quickly. Even if you have mild symptoms, don’t attempt to ride out a virus on your own, and don’t assume that coughing is the only clue you’ve got COVID-19. You should contact your doctor if you have body aches, fever, a sore throat, or respiratory symptoms so you can be tested for COVID-19. The list of warning signs for the coronavirus is continually expanding and now includes loss of taste or smell, nausea, diarrhea, or even swollen red toes.It’s important to know which infection you have. With the flu, your doctor can prescribe an antiviral medication. But if you have COVID-19, your doctor will help you decide if you need to go to the hospital for severe symptoms where you might be prescribed steroids or other experimental medications. Plus, you’ll have to be quarantined to avoid transmitting it to others.You might not think the flu is a big deal if you get a mild case, where you feel under the weather for a few days and your symptoms go away on their own. But just ask someone who’s recovered from viral pneumonia caused by the flu to understand how miserable you can be. It can also land you in the hospital. I don’t think people appreciate how severe it can be.