The fall signals the start of the flu season, which, along with the COVID-19 pandemic, some are calling a “twindemic.” How and why should people protect themselves from influenza? Keck Medicine of USC family medicine physician Anjali Mahoney, MD, answers questions about staying healthy this flu season.

Q. When is the best time to get a flu shot?

A. The influenza (commonly known as the flu) season usually starts in October and peaks around January or February. The best time to get a flu shot is in September to give your body a chance to mount an immune response to the virus should you be exposed to it.

Q. Who should get a flu shot?

A. Everyone over the age of six months should get a flu shot. It is especially important that people over 65, under two or who are immunocompromised get vaccinated as they are most vulnerable to severe complications from the flu.

Those over 65 receive a special high dose flu shot four times as powerful as a regular flu shot because this age group experiences more flu-related deaths and hospitalizations than any other. Older adults are especially susceptible to the flu because as we age, our immune systems weaken, making us more vulnerable to illnesses.

Q. Is it safe to get a flu shot?

A. Absolutely. Some people worry they might catch the flu from the shot, but the vaccine is not live, so that is unlikely. The vaccine does cause the body to mount an immune response, so occasionally people may develop a low-grade fever or body aches, but this typically only lasts a day or two. Some people also report tenderness in the arm where the shot was given.

Q. How effective is the flu vaccine?

A. Every year the Centers for Disease Control looks at the different flu viruses circulating in the community and creates a vaccine to protect against the most common flu strains. In general, the vaccine is 40% to 60% effective in preventing the flu, with some years more effective than others. In addition, if people who are vaccinated catch the flu, their cases tend to be milder than those who are not vaccinated.

Q. How does the COVID-19 pandemic affect flu season?

A. The pandemic makes it even more important to get a flu shot this year. Both viruses can do serious damage, and you want to avoid getting both diseases at the same time or back to back. In addition, by getting a flu shot, you help protect others in the community from catching the flu, which is especially key for vulnerable populations such as those with compromised immune systems, the very young or older adults. You also avoid putting a strain on already taxed health care workers and systems battling the coronavirus should you need medical attention due to complications from influenza.

Q. If someone starts to feel sick, how can they tell if it is the flu or COVID-19?

A. The two viruses can present the same way, but there are differences. With the coronavirus, people might lose their sense of smell and taste, and we do not see these symptoms with the flu. In addition, the flu typically hits more suddenly and harder, with a high fever, chills and possibly nausea and vomiting, which is less common with COVID-19. If you suspect you have either virus, contact your care provider immediately. For the flu, if you are treated within the first 48 hours, your doctor may be able to prescribe medication to reduce the length of sickness.

Q. Could increased masking for COVID-19 help stop the spread of the flu this season?

A. Possibly. However, keep in mind that as with COVID-19, a mask is only one form of protection and is not 100% effective. The best protection against the flu is getting the vaccine and practicing good hygiene such as hand washing.

Q. Is there any other advice you would offer people as we head into the “twindemic”?

A. I would urge people to continue the good habits they have adopted while protecting themselves from COVID-19—washing their hands frequently for 20 seconds at a time, disinfecting surfaces routinely, and avoiding crowds. While we may be facing two viruses at once, these practices will help keep us healthy in the months to come.