With flu season swiftly approaching in a country already battling a resurgence of the coronavirus, experts are urging Americans to avail themselves of any and all vaccines they are eligible for — whether it’s their first coronavirus vaccination, a booster vaccine dose to combat waning immunity or a flu shot.

“It’s terribly important” to get both the flu and coronavirus vaccines, said William Schaffner, medical director of the National Foundation for Infectious Diseases. “They are both very nasty respiratory viruses that can make many people very, very sick.”

And because the coronavirus and flu vaccines “train your immune system to protect you against completely different viruses,” getting a shot that protects you against one virus will not offer any protection against the other, said Kelly Moore, president and CEO of the Immunization Action Coalition.

“It’s like protecting yourself against a bee and a wasp, both of which can sting you,” Schaffner said. “You’ve got to protect yourself against each one separately.”

The Centers for Disease Control and Prevention recommends that everyone be vaccinated against the flu by the end of October. This year, that time frame could overlap with the period when many Americans may become eligible for a booster dose of the coronavirus vaccine.

Extra doses of coronavirus vaccine are already being administered to immunocompromised people. Despite some disagreement among experts about the need for additional shots at this time, the Food and Drug Administration and the CDC have green-lit boosters for certain groups of at-risk Americans who received the two-dose Pfizer-BioNTech coronavirus vaccine. (The agencies are awaiting more data before making recommendations about boosters for people who received the Moderna and Johnson and Johnson vaccines.)

The FDA recently authorized a third shot of the Pfizer-BioNTech vaccine for people 65 and older; those 18 to 64 at high risk of severe illness; and those 18 to 64 whose “frequent institutional or occupational exposure” to the coronavirus puts them at high risk of covid-19 complications, including teachers, health-care workers and grocery store employees.

The CDC has backed the authorization, recommending a third shot of the Pfizer-BioNTech vaccine for people 65 and older, nursing home residents and those 50 to 64 with underlying medical conditions six months after receiving their second dose from the initial vaccination. The agency added that younger people, 18 to 49 years old, with underlying medical conditions may assess their own risk and choose to get a booster if they want one. CDC Director Rochelle Walensky also included a recommendation that people ages 18 to 64 who are at increased risk of being exposed to or transmitting the coronavirus because of their jobs receive a booster shot.

As Americans prepare to roll up their sleeves again for flu vaccines and possibly coronavirus boosters, here’s what experts say you need to know.