Several types of flu vaccines are available in the United States, and all of them are now trivalent, meaning they protect against three strains of influenza. The shift from four-strain (quadrivalent) vaccines happened for the 2024-2025 season because one of the influenza B lineages, B/Yamagata, stopped circulating. Every current flu vaccine includes an influenza A(H1N1), an A(H3N2), and a B/Victoria-lineage virus.
Which vaccine you’ll be offered depends mainly on your age and whether you have specific health considerations like an egg allergy. Here’s what’s out there.
Standard Flu Shots
Most people end up getting a standard-dose inactivated flu shot. These are the workhorses of flu season, approved for anyone six months and older, and they come from several manufacturers using slightly different production methods. The majority are made using egg-based processes, which is the traditional approach that’s been used for decades. These are widely available at pharmacies, clinics, and doctor’s offices, and they’re what you’ll typically receive unless you request or qualify for something specific.
Cell-Based and Recombinant Options
Two flu vaccines are completely egg-free: Flucelvax, which is cell-based, and Flublok, which is recombinant. These matter most for people with egg allergies, though anyone in the approved age range can get them.
Flublok uses a recombinant manufacturing process, meaning it’s made with synthetic proteins rather than growing the virus in eggs or cells. The FDA approved it for people ages 9 and older. It’s also one of three vaccines specifically preferred for adults 65 and older, based on evidence suggesting it may work better than standard-dose options in that age group.
Flucelvax is grown in animal cells instead of eggs. Both egg-free vaccines avoid the slight changes to the virus that can occur during egg-based production, which some researchers believe could translate to a better immune match. For most healthy adults under 65, though, there’s no official preference for one type of flu vaccine over another.
Vaccines Preferred for Adults 65 and Older
Older adults have weaker immune responses to standard flu vaccines, so three options are specifically recommended for people 65 and up:
- Fluzone High-Dose: Contains a higher amount of the active ingredient to provoke a stronger immune response.
- Fluad: A standard-dose vaccine that includes an adjuvant (an ingredient called MF59 that boosts the immune response). It’s egg-based and manufactured by Seqirus.
- Flublok: The recombinant, egg-free vaccine described above.
Studies suggest all three are potentially more effective than standard-dose vaccines in this age group. If you’re 65 or older and your pharmacy or clinic doesn’t carry one of these, it’s worth asking if they can order it. Side effects are comparable across the three. A clinical trial found that injection-site pain limiting normal activity was no more common with Fluad than with Fluzone High-Dose, and overall safety was similar.
The Nasal Spray Vaccine
FluMist is the only flu vaccine given as a nasal spray rather than a shot. It uses a live but weakened virus and is approved for people ages 2 through 49. In September 2024, the FDA approved FluMist for self-administration or caregiver administration, meaning you may be able to use it at home rather than visiting a clinic.
FluMist isn’t an option for everyone. You should avoid it if you’ve had a severe allergic reaction to any flu vaccine component (including egg protein), or if you’re a child or teenager taking aspirin, because of the risk of Reye’s syndrome when aspirin and live influenza virus interact. Pregnant people and those with weakened immune systems are also generally directed toward inactivated shots instead.
Thimerosal and Preservative Concerns
Thimerosal, an ethyl mercury-based preservative, is only found in multi-dose vials, the large vials that clinics draw several individual shots from. It prevents bacterial contamination in those shared containers. Most single-dose vials and prefilled syringes do not contain thimerosal, and neither does FluMist. If this matters to you, simply ask for a single-dose vial or prefilled syringe. They’re widely available.
Children and Two-Dose Schedules
Children ages 6 months through 8 years may need two flu shots in a single season, spaced at least four weeks apart. This applies if they’ve never received a flu vaccine before, if their vaccination history is unknown, or if they haven’t previously received at least two doses of seasonal flu vaccine in any prior season. Children who’ve already been through that initial two-dose series only need one shot per year going forward.
Because of the four-week gap between doses, children who need two shots should get their first dose as soon as the vaccine becomes available, ideally in September. This ensures they’re fully protected before flu activity peaks.
When to Get Vaccinated
September and October are the ideal months for most people. Protection from the vaccine peaks within a few weeks and gradually declines over the following months, so getting vaccinated too early (July or August) can leave you less protected late in flu season. Adults 65 and older and people in the first or second trimester of pregnancy are especially encouraged to wait until September rather than vaccinating in the summer.
Exceptions: children who need two doses should start as early as the vaccine is available, and people in the third trimester of pregnancy can reasonably get vaccinated during July or August if that timing works better. Vaccination remains worthwhile throughout the season, even into January or later, as long as flu viruses are still circulating.
How Well Flu Vaccines Work
Flu vaccine effectiveness varies by season depending on how well the vaccine strains match what’s actually circulating. During the 2023-2024 season, vaccination reduced the risk of outpatient flu illness by roughly 35 to 47 percent in adults. For hospitalizations, the reduction was around 39 to 40 percent in adults.
Children benefit more. In the same season, flu vaccination cut outpatient illness by 56 to 65 percent in kids ages 6 months through 17 years, and reduced hospitalization risk by 58 to 64 percent. Even in years when effectiveness is moderate, vaccination consistently reduces the severity of illness if you do get infected.
Cost and Insurance Coverage
Most health insurance plans cover the flu vaccine with no out-of-pocket cost. Medicare Part B covers one flu shot per season, and you pay nothing if your provider accepts Medicare assignment. If you have a Medicare Advantage plan, coverage details may vary, so check with your plan. For people without insurance, retail prices at pharmacies typically range from about $25 to $75 depending on the vaccine type, though discount programs and community health centers often offer lower-cost or free options.