This year's seasonal flu vaccines each provide protection against four of the influenza viruses expected to be most common during this flu season. High-dose flu vaccines will be available for adults age 65 and older. Vaccines will be offered as an injection and as a nasal spray.

Influenza, often called the flu, is an infection of the nose, throat and lungs, which are part of the respiratory system. The flu is caused by a virus. Most people with the flu get better on their own. But influenza can cause serious complications for some groups of people.

In general, people at higher risk than average for complications are young children, especially children age 12 months and younger, pregnant people, adults over age 65 and people with certain medical conditions.

Getting an influenza vaccine, though not 100% effective, is the best way to prevent the misery of the flu and its complications. The Centers for Disease Control and Prevention (CDC) recommends annual flu vaccination for everyone age 6 months or older.

The flu vaccine can lower your risk of getting the flu. It also can lower the risk of having serious illness from the flu and needing to stay in the hospital or dying from the flu.

Here are the answers to common questions about flu shots:

Private manufacturers make the flu vaccine. It takes about six months. The availability of the flu vaccine depends on when production is completed. But generally, shipments begin sometime in August each year in the United States. Healthcare professionals may begin vaccinating people as soon as the flu vaccine is available in their areas.

It takes up to two weeks to build immunity after a flu shot.

You can benefit from the vaccine even if you don't get it until after the flu season starts. It's usually best for people in the United States to get the flu vaccine in September and October. Aim to get it by the end of October. But you can still protect yourself against late flu outbreaks if you get the vaccine in February or later.

Because flu viruses change so quickly, last year's vaccine may not protect you from this year's viruses. New flu vaccines are released every year to keep up with rapidly changing flu viruses.

When you get vaccinated, your immune system makes antibodies to protect you from the viruses included in the vaccine. But antibody levels may decline over time — another reason to get a flu shot every year.

The CDC recommends annual influenza vaccinations for everyone age 6 months or older. Although the annual influenza vaccine isn't 100% effective, the vaccine lowers the chances of having severe complications from infection. This is especially true for people who are at high risk for flu complications.

High risk groups include:

• Adults older than age 65.
• People in nursing homes or long-term care, as well as people who are in the hospital.
• Young children, especially those age 12 months or younger.
• People who plan to be pregnant, are pregnant or recently gave birth during flu season.

And in the United States, some groups have a higher risk of needing treatment in the hospital for flu. Those groups include people who are American Indian or Alaska Native, Black or Latino.

Other groups at high risk for flu complications include people with:

• Weakened immune systems.
• A body mass index (BMI) of 40 or higher.
• Nervous system disorders or conditions that change how the brain processes information.

And people with certain medical conditions have a higher risk of flu complications, such as:

• People who have chronic illnesses, such as asthma, heart disease, kidney disease, liver disease and diabetes.
• People who have had a stroke.
• People who are younger than 20 years of age and are receiving long-term aspirin therapy.

Children between 6 months and 8 years may need two doses of the flu vaccine, given at least four weeks apart, the first time they are given a flu vaccine. After that, they can receive single annual doses of the flu vaccine. Check with your child's healthcare professional.

Also, check with your healthcare team before receiving a flu vaccine if you had a severe reaction to a previous flu vaccine. The flu vaccine isn't recommended for anyone who had a severe reaction to a previous flu vaccine. Check with your healthcare professional first, though. Some reactions might not be related to the vaccine.

If you have an egg allergy, you can receive any of the flu vaccines, anywhere the vaccine is offered.

The flu vaccine will be available as a shot, also called an injection, or as a nasal spray.

The nasal spray vaccine is approved for people between 2 and 49 years old. The nasal flu vaccine isn't recommended for some people, including:

• People who had a severe allergic reaction to a flu vaccine in the past.
• Pregnant people.
• Children age 17 years or younger who are taking aspirin or a salicylate-containing medicine.
• People with weakened immune systems and caregivers or close contacts of people with weakened immune systems.
• Children between ages 2 and 4 years old diagnosed with asthma or wheezing in the past 12 months.
• People who recently took antiviral medicine for the flu.
• People with a cerebrospinal fluid leak or the potential for a leak, as with a cochlear implant.

Check with your healthcare team to see if you need to be cautious about getting a nasal spray flu vaccine.

You also can get the flu vaccine as a shot that's usually given in a muscle in the arm. If you're an adult under 65, you can choose to get your vaccine with a jet injector device, which uses a high-pressure, narrow stream of fluid to go through the skin instead of a needle.

No, the flu vaccine can't give you the flu. The flu vaccine also doesn't increase your risk of COVID-19. But you might develop flu-like symptoms — despite getting a flu vaccine — for many reasons, including:

• Reaction to the vaccine. Some people have muscle aches and a fever for a day or two after receiving a flu vaccine. This may be a side effect of your body's production of protective antibodies.
• The two-week window. It takes about two weeks for the flu shot to take full effect. If you're exposed to the influenza virus shortly before or during that time period, you might catch the flu.
• Mismatched flu viruses. In some years, the influenza viruses used for the vaccine don't match the viruses spreading during the flu season. If this occurs, your flu shot will be less effective. But it may still offer some protection.
• Other illnesses. Many other illnesses, such as the common cold, also have flu-like symptoms. So you may think you have the flu when you actually don't.

How well the flu vaccine works to protect you from the flu can vary. The standard flu vaccine is generally more effective among people younger than 65. Some older people and people with certain medical conditions may develop less immunity after receiving a flu shot.

High-dose flu vaccines are a type of vaccine approved for people age 65 and older. They can help people in this group have a stronger immune system response against flu viruses.

Reviews of past studies have found that the flu vaccine lowers the risk of flu illness by 40% to 60% when the vaccine matches the spreading flu viruses.

Even when the vaccine doesn't completely prevent the flu, it may lessen the severity of your illness. It also may lower the risk of serious complications and serious illness needing hospital stays.

Flu vaccination is especially important because the flu and coronavirus disease 2019 (COVID-19) cause similar symptoms. Both COVID-19 and the flu may be spreading at the same time. Vaccination is the best way to protect against both.

And if a COVID-19 vaccine or booster and a flu vaccination end up due at the same time, the CDC reports that you can get vaccinated for both in one visit.

The flu vaccine is your best defense against the flu. But there are more steps you can take to help protect yourself from the flu and other viruses, including COVID-19.

Follow these standard precautions:

• Wash your hands. Wash your hands often and thoroughly with soap and water for at least 20 seconds. Use an alcohol-based sanitizer on your hands if soap and water aren't available.
• Keep your hands away from your face. Avoid touching your eyes, nose or mouth.
• Avoid crowds. The flu spreads easily where people are gathered, for example in school or on public transportation. Avoid crowds when the flu or COVID-19 is spreading in your area.
• Cover your coughs and sneezes. Cover your mouth with a tissue or the inside of your elbow when you cough or sneeze, and then wash your hands.
• Regularly clean and disinfect commonly touched surfaces, such as counters, light switches and doorknobs. This can help to prevent the spread of infection from touching a surface with the virus on it and then touching your face.
• Practice good health habits. Get regular exercise, get enough sleep, drink plenty of fluids, eat a healthy diet and manage stress.

Avoid close contact with people who are sick if you can. If you become sick with the flu, you also can help prevent the spread of the flu by staying home and away from others. Continue staying home until your fever has been gone for at least 24 hours.

Getting your flu vaccine can lower your risk of the flu and its complications. Following these precautions can help protect you from the flu or other respiratory illnesses.