Most people can benefit from getting vaccinated against the flu. The type of vaccine that’s best for you may vary depending on your age and some other factors.

Flu season in the United States is between October and May each year. Consider getting a flu shot as early as October to protect yourself. On average, flu vaccines take about 2 weeks to begin providing protection.

The flu is a highly contagious respiratory condition that causes a range of symptoms, such as:

  • sore throat
  • coughing
  • runny nose
  • fatigue
  • chills
  • body aches
  • headache

Some cases of the flu are mild, and symptoms often resolve in 7 to 10 days. But in other cases, the flu can progress and cause a secondary infection, such as bronchitis, pneumonia, or an ear infection. Life threatening complications can occur in certain groups of people, including those who have a weakened immune system and those ages 65 years and older.

Flu vaccines are 40% to 60% effective when the virus type in the vaccine aligns with the circulating virus. If you do contract the flu after getting the vaccine, your symptoms may be less severe than they would have been without vaccination.

Flu shots are safe for most people ages 6 months and older. Here’s a look at the different types of flu shots, as well as information on who is eligible for each type.

Trivalent flu vaccines protect against three strains of the virus:

  • influenza A (H1N1)
  • influenza A (H3N2)
  • an influenza B virus

Options are below.

Regular standard-dose trivalent shots

These are egg-grown flu vaccines given by injection into a muscle in your arm. Standard-dose vaccines are for people 18 to 64 years old.

Trivalent and quadrivalent shots made with adjuvant

These shots, called Fluad (trivalent) and Fluad Quadrivalent, are approved for people ages 65 years and older. They include an ingredient called adjuvant, which creates a stronger immune system response.

These vaccines are slightly different because they protect against four strains of the flu virus (two influenza A viruses and two influenza B viruses). As a result, they can provide broader protection from infection.

As of the 2024 to 2025 flu season, all available flu vaccines are trivalent. According to the World Health Organization (WHO), quadrivalent flu vaccines are not currently in use. This is because public health precautions during the COVID-19 pandemic effectively eliminated one of the four flu strains previously included in those vaccines.

Manufacturers update flu vaccines each year to protect against the strains of flu that are most common at that time, and quadrivalent vaccines may return in the future.

Some of the following vaccine types are still available in trivalent forms.

Regular standard-dose quadrivalent shot

The standard-dose flu shot is available to people ages 6 months and older. There’s also the option of a quadrivalent shot that contains the virus grown in a cell culture. This type of vaccine is also available to people 6 months old and older.

High dose quadrivalent shot

The high dose quadrivalent vaccine (Fluzone) is designed specifically for people ages 65 years and older. Flu-related complications increase with age because older people have a weaker immune system.

Fluzone contains four times as much flu virus antigen as a standard-dose shot. (Antigen is the part of the vaccine that stimulates your immune system to respond and protect against the flu virus.)

A high dose vaccine is recommended for older adults because up to 85% of flu-related deaths occur in people 65 years and older.

Jet injection quadrivalent shot

Afluria Quadrivalent is a type of flu shot now approved for injection by needle for people ages 6 months and older or by jet injector for people 18 to 64 years old.

A jet injector is a medical device that uses a high pressure stream of fluid, rather than a needle, to deliver medication under the skin.

Recombinant quadrivalent shot

This vaccine is not manufactured or grown from eggs, so it’s a suitable alternative for people who have severe egg allergy. It’s approved for people ages 18 years and older.

Live attenuated intranasal spray

This vaccine is made using eggs and given as a nasal spray in people 2 to 49 years old who are not pregnant.

It includes a dose of attenuated flu viruses. Instead of killed flu, this type of vaccine contains severely weakened flu viruses that cannot cause a widespread infection.

You should not receive this type of vaccine if you:

  • are pregnant
  • are outside the recommended age range
  • have a weakened immune system or are a caregiver for someone who does
  • have had a serious allergic reaction to any ingredient in this vaccine or another flu vaccine
  • have recently taken antiviral medications for the flu
  • have a cerebrospinal fluid leak
  • have cochlear implants
  • do not have a working spleen

Children 2 through 17 years old should not get this vaccine if they’re currently taking medications containing aspirin or salicylate. And children 2 through 4 years old should not receive it if they have asthma or have experienced wheezing in the last 12 months.

If any of the following conditions applies to you, talk with a doctor before receiving this vaccine to make sure it’s safe for you:

  • You have asthma or another condition that can increase your risk of serious flu complications.
  • You’re currently not feeling well.
  • You previously developed Guillain-Barré syndrome after receiving a flu vaccine.

As with other types of vaccines, there’s a risk of side effects with the flu shot. Common side effects may include tenderness and redness or other discoloration at the injection site.

Some people also experience mild flu-like symptoms for 1 to 2 days after vaccination. You might experience weakness, body aches, or a fever, but these symptoms do not mean you have the flu.

If you have a severe allergy to eggs or another ingredient in the vaccine, you might experience an allergic reaction.

Signs of a serious reaction include:

  • difficulty breathing
  • wheezing
  • hives
  • fast heartbeat
  • dizziness

Life threatening allergic reactions after getting the flu shot are rare.

Symptoms of a reaction can begin within a few minutes to a few hours of vaccination. If you have symptoms of an allergic reaction, seek medical attention right away.

The Centers for Disease Control and Prevention (CDC) recommends that people with an egg allergy still get a flu shot. You can ask for a vaccine that doesn’t contain egg protein.

The CDC also generally recommends that people receive flu shots in a medical setting where healthcare professionals can recognize and treat an allergic reaction if necessary.

You might not be able to get a flu vaccine if you’re allergic to a vaccine ingredient other than egg.

In rare cases, Guillain-Barré syndrome may develop within days or weeks of a vaccination.

Guillain-Barré syndrome is a neurological disorder in which your immune system attacks your peripheral nervous system. It can cause muscle weakness and paralysis.

Among every 1 million people who receive a vaccination, only one or two cases of Guillain-Barré may occur each year.

Getting an annual flu vaccination is one of the best ways to protect yourself from the flu virus.

The flu can lead to complications in people who have a weakened immune system, such as young children, older adults, and those with chronic health conditions.

Talk with your doctor about which flu vaccine is right for you, and get vaccinated as early as possible for each annual flu season.