Flu (Seasonal Influenza)

Anyone 6 months of age or older should get a flu vaccine. The vaccine is especially important for people at high risk of serious flu complications. High risk people include:

• Young children
• Pregnant people
• People who are 65 years and older
• People with chronic health conditions like asthma, diabetes, heart, and lung disease

Talk to a health care provider about getting your flu vaccine each year and what is best for you.

No, the flu vaccine cannot give you the flu. Vaccines use a dead, weakened, or harmless part of a germ to teach your body how to fight it, if you get sick.

A flu vaccine is the only way to protect yourself against all 3–4 strains expected to spread that season. After recovering from flu, you have protection against only that one strain. Talk to a health care provider about vaccination options and what is best for you.

A person will gain immunity against the flu after getting a vaccine or in some cases after they recover from the flu. It is important to remember that the flu can cause very serious illness in some people. The risk from getting a vaccine is much less than the risk of getting sick with the flu.

It takes about two weeks after vaccination for the flu vaccine to provide full protection. During this time, it’s important to take additional precautions, such as washing your hands often with soap and water for at least 20 seconds, cleaning frequently touched surfaces often, and mask if you need.

We recommend annual flu vaccines for all people ages 6 months and older for two reasons: 

1. Flu vaccine becomes effective approximately 2 weeks after receiving the vaccine, and protection peaks 2-3 months after vaccination, wearing off after about 6 months. Unfortunately, that means last year’s flu vaccine doesn’t provide much protection. 
2. Different flu strains circulate every year, and the flu vaccine is designed to try to target those circulating strains.  

For most adults and older children, the flu vaccine is actually “boosting” our immunity to flu, since we have had the flu before and may also have been vaccinated before. For adults and children age 9 years or older, it is therefore recommended to get only one dose of flu vaccine.

However, younger children may never have had the flu or flu vaccine before, and are also at highest risk for severe complications from flu. It is therefore recommended that children ages 6 months to 8 years who have not had at least two prior doses of flu vaccine get 2 doses of the flu vaccine, 4 weeks apart. 

The flu is primarily transmitted by larger respiratory droplets when someone with the flu coughs or sneezes. Wearing a simple surgical mask protects against transmission when the flu virus is in a larger respiratory droplet. 

Flu can also less commonly be transmitted via smaller aerosolized particles: breathing and talking. An N95 mask protects against transmission via aerosols.  

This means that wearing a surgical mask or an N95 respiratory does protect against flu transmission. We recommend masking in crowded indoor settings when flu cases are high, particularly for people at high risk for severe illness. 

In addition to masking, we recommend vaccination for all individuals ages 6 months and older because: 

• Masking, particularly for long periods of time, can be challenging for some people due to discomfort.  

• Masking is subject to user error (e.g. improper fit or removal). 

• Masking is not feasible as a protection strategy is some settings (e.g. young children in childcare settings, in the home when a family member is ill).  

In summary, we recommend both vaccination and masking as measures to reduce the risk of severe influenza infection.

The flu vaccine each year is designed to protect against the three influenza viruses that research indicates will be most common during the upcoming season. The flu vaccine formulation has to be decided about 6 months before flu season starts, in order to given manufacturers time to produce the vaccine. 

This year there is a mismatch between the vaccine that was developed and the most common circulating strain of flu virus, H3N2 subclade K, because it emerged after this year’s shot was produced. 

But even without a perfect match, this year’s vaccine provides important protection against serious flu-related complications, including hospitalization and death because: 

• The flu vaccine causes the body to make antibodies. 

• A mismatched vaccine still provides cross protection, antibodies can recognize and fight against slightly different strains of influenza than those that are in the vaccine. 

• A mismatched vaccine can boost your existing immunity to flu, so if you been infected or vaccinated with a strain similar to subclade K (or any other type of flu) in the past, the vaccine helps strengthen your immunity going into flu season 

• Multiple strains of flu circulate each flu season, so the protection provided by the flu vaccine (which contains three strains) can help in the event of exposure to strains other than subclade K. 

In fact, even with the mismatch, studies show that this year’s vaccine reduces hospitalizations by 70–75% in children and offers 30–40% effectiveness in adults.  

Vaccination is still highly recommended to prevent serious flu-related outcomes.