How long does the flu shot last?

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The flu shot offers protection against the flu for at least 6 months. Healthcare professionals usually vaccinate most people in October, when flu activity typically begins to increase, so their immunity will last until the following April.

In people aged 65 years and over, the effects of the flu vaccine may wear off earlier than usual, leaving them at higher risk than younger people of severe illness. The reason for this is that as people get older, their immune response to vaccines weakens.

According to the Centers for Disease Control and Prevention (CDC), a yearly flu shot is recommended for everyone aged 6 months or older.

Therefore, most individuals should get a flu shot once a year. Researchers adjust each yearly flu vaccine, depending on what strain of flu they predict will be common during that season. As a result, the flu shot is different each year. Some children will need two doses of the flu vaccine per season, which they should receive at least 4 weeks apart.

A 2018 study found that previous flu vaccination in children did not reduce the effectiveness of future flu shots, which supports the recommendation for yearly flu vaccination in children.

In the United States, flu cases begin to increase in October and are highest between December and February. However, a person can still get sick from the flu as late as May. The exact timing of the flu season varies from year to year.

According to the CDC, the best time to get a flu shot is by the end of October. However, individuals can get a flu shot at any time of the year. It is still better to get the shot as early as September or as late as January than not to get one at all.

If someone gets a flu shot too early, the vaccine may not last the entire flu season. A person should ask a doctor when they should have a flu shot, especially if they have any underlying health conditions or are aged 65 years or over.

Once an individual gets the flu shot, it takes 2 weeks to start working. The vaccine stimulates an immune response, whereby white blood cells identify the flu virus and begin making antibodies.

These antibodies will only circulate a person’s body for about 6 months. However, after they break down, the B lymphocytes can make the antibodies quicker the next time they encounter the virus.

There are two types of flu shot:

Inactivated vaccine

The flu shot contains an inactivated version of the flu virus. It may be easier for a person to think of the virus as dead.

Recombinant vaccine

The flu shot contains a single gene of the flu virus but not the full genetic copy.

The flu shot is the best prevention against getting the flu. The effectiveness of the flu vaccine depends on various factors, including:

• Age: The vaccine is less effective in individuals at or over the age of 65 years.
• Virus mutation: The virus could change and no longer match the vaccine.
• Vaccine schedule: Immunity to the flu may only last up to 6 months because as more time passes, more flu antibodies degrade.

Side effects from the flu shot are typically minor. They may include:

• soreness
• swelling
• fever
• minor muscle aches
• a headache
• nausea
• low grade fever

When a person has a flu shot, the side effects typically present quickly and last 1–2 days.

Flu vaccines cannot cause the flu as the vaccine contains either an inactive form of the virus or only part of the virus’s genetic material.

The vaccine aims to cause an immune response, not a flu infection.

Serious allergic reactions to flu vaccines are very rare. There is an extremely small possibility that a person could develop Guillain-Barré Syndrome (GBS) after receiving the vaccine. Some individuals who have had GBS should not get a flu shot.

Getting the flu vaccine reduces the likelihood of getting the flu. This illness can lead to severe complications, such as pneumonia.

Each year, 291,000–646,000 people die worldwide from seasonal flu-related respiratory illnesses. Getting yearly flu shots will help prevent many of these deaths.

Getting vaccinated offers society many health benefits. These include:

• preventing millions of flu-related doctor’s visits each year
• lessening the severity of the flu
• lowering the number of sick days at work or school
• reducing flu-associated hospitalizations
• producing herd immunity
• reducing flu deaths

Learn more about the benefits and risks of the flu shot here.

The flu is a potentially severe illness that primarily affects the respiratory tract, including the lungs. The highly contagious influenza virus causes it. Symptoms of the flu typically come on suddenly and include fever, body aches, and a cough.

The flu can be lethal, especially in certain groups of people, including:

• young children
• older adults
• those with underlying health issues

Experts recommend yearly flu shots for flu prevention for people who are at least 6 months old. The best time to get a flu shot is by the end of October.

The benefits of the flu shot include prevention against the flu and its potentially lethal complications. Any side effects of the flu shot are usually mild.