The relatively low numbers last year may be attributed to several factors: either the COVID-driven safety precautions - like mask wearing, physical distancing and washing hands - helped reduce the spread of the flu and other respiratory diseases, or the annual vaccine formula was especially effective against the variants of influenza virus in circulation.

The severity of flu seasons is hard to predict with certainty. Some light seasons may be followed by light or severe influenza numbers, so it's a good idea to get a shot either way every year for family member ages 6 months and up.

"Much like during the 2020 season, influenza-like-illness activity remained historically low in 2021 for Southern Hemisphere countries. This could signal another mild season for the U.S.," said Ellison, who is a doctor of pharmacy and the military lead for the DOD Influenza Program.

However, while encouraging, "it's not that simple," Ellison said.

"As more people are vaccinated for COVID and localities begin to further roll back restrictions on mask wearing and social distancing, more people could be exposed to other viruses including influenza," Ellison said.

"Given the low influenza case rate in 2020-2021 in the U.S., not as many people were exposed to the flu," last year, Ellison said. "This creates something called an 'immunity debt,' meaning the immune system may have a harder time when individuals encounter the flu virus again. Due to this, the flu virus may more readily infect and potentially cause more severe disease in unvaccinated individuals."

Although it's not certain, some models predict that due to this "immunity debt," there may be a large compensatory flu season this winter. "The best way to get out of this 'immunity debt' is to build up your immunity, and the best way to do that is to get your annual flu shot," he explained.

There are nine options for flu vaccination in the U.S., including an intranasal spray. There are two egg-free products available although the CDC guidance says that people with a history of egg allergy of any severity can receive any licensed flu vaccine as long as it is age-appropriate and recommended for the season. There are also vaccines specifically created to address the over-65 population.

Vaccinate Children and At-Risk Populations as Soon as Possible

"One major item to consider is that on the spectrum of common childhood illness, flu is more dangerous than the cold," Ellison said.

"Kids under five and particularly those less than two years old are at a higher risk of having flu-related complications like pneumonia or dehydration that could require hospitalization or worse. Flu vaccine is the best way to prevent this," Ellison said.

According to the CDC, children can get vaccinated as soon as vaccine becomes available. Some children need two doses. For those children, the CDC recommends to get the first dose as soon as a vaccine is available because the second needs to be given at least 4 weeks after the first.

"There is a wealth of data demonstrating that flu vaccine is safe during pregnancy, and vaccination during pregnancy is important because pregnant people are at higher risk of getting severe flu due to changes in many of the body's systems," Ellison said.

"It's important to note that many of these changes persist for up to two weeks postpartum, so even after giving birth the individual remains at higher risk for a while. Not only that," he said, "but the flu vaccine helps protect both the parent and the baby from flu while still developing and after they are born through antibodies passed along from the mother to the baby." Early vaccination can also be considered for people who are in the third trimester of pregnancy, because this can help protect their infants during the first months of life (when they are too young to be vaccinated), the CDC noted.

Some other people who are at higher risk of infection include those who are 65 and older, those with asthma, heart disease, diabetes, suppressed immune systems, as well as other medical conditions.

According to the CDC, those people who have suspected or confirmed COVID-19, whether or not they have symptoms, should wait until they have met the criteria to discontinue isolation before getting a flu shot.

"For those with mild COVID-19 symptoms or no symptoms," Ellison said, "this really doesn't have anything to do with COVID-19 infection interfering with the flu vaccine effectiveness."

"It is really an important precautionary measure to avoid exposing health care personnel and other patients to COVID-19. With the high transmissibility of some of the COVID-19 variants, it is vitally important that those infected with COVID-19 do their best to prevent exposing other people to the virus," Ellison said.

DOD immunization sites are paying close attention and adhering to the most recent guidance from the CDC to safely administer flu shots this season as the COVID-19 pandemic continues. Procedures at immunization sites are subject to change as the CDC guidance is reassessed and updated, so it is best to check with the local MTF on the current safety requirements in place before heading to the facility for a flu shot, Ellison recommended.