Can You Get a Flu Shot While Sick?

You can get a flu shot while sick if you have mild symptoms and no fever. Most healthcare providers feel it is best to get your flu shot early since it takes time to build immunity after you've received it. This means getting it when you have mild symptoms may be better than putting it off until you recover.

According to the Centers for Disease Control and Prevention (CDC), people who are moderately or severely ill should wait until they recover before getting vaccinated. This is because the flu shot is made of inactivated (dead) viruses that stimulate the production of protective antibodies. If you are really sick, your immune system will be less able to produce enough antibodies to protect against influenza A and B.

What Happens When You Get a Flu Shot While Sick?

It is safe to get a flu shot if you have a mild cold with symptoms like a runny nose and a sore throat.

Being moderately or severely ill, however, temporarily weakens the immune system. If you're sick when you get the flu shot, your immune system is already fighting the other illness or infection. This means it may not have the resources to also produce an immune response against the flu.

If you are ill, the flu shot could also slow your recovery from the other illness because your immune system is dividing its resources.

How Does the Flu Shot Work?

Vaccines are designed to stimulate a protective immune response. The flu shot contains influenza (flu) viruses that have been killed. These are called inactivated vaccines.

When these dead viruses are injected into your body, your immune system responds as if the viruses are alive by producing antibodies. These antibodies recognize and defend against the specific viruses you were injected with.

A person's response to a vaccine may not always be strong enough to provide ample immune protection. Other things besides illness can undermine the response, such as undergoing chemotherapy, taking immunosuppressants, or having untreated HIV. All these are associated with a weakened immune response.

When Should You Get the Flu Shot?

Having cold symptoms isn't necessarily a reason to avoid the flu shot. Most people, even children, can get the shot if their symptoms are mild.

According to the CDC, it is perfectly fine to get a flu shot if you have:

• A low-grade fever (no more than 101 F)
• A cold, runny nose, sore throat, or cough
• An ear infection (otitis media)
• Mild diarrhea
  

When to Postpone the Flu Shot

The is no clear line between when a sickness is "mild" or "moderate." If you are unsure (or feel that your symptoms may be getting worse), err on the side of caution and delay vaccination until you feel better.

One of the main indications that you should postpone the flu shot is a moderate to high fever. In adults, this is generally when fever exceeds 102 F.

Severe diarrhea, vomiting, coughing up phlegm, or severe fatigue or malaise (a general feeling of unwellness) are also strong reasons for postponement.

If in doubt, call your healthcare provider or your child's pediatrician for advice.

Who Needs the Flu Shot

Certain groups at high risk for flu complications should be vaccinated, This reduces the risk of complications like pneumonia, myocarditis (heart inflammation), encephalitis (brain inflammation), rhabdomyolysis (the destructive breakdown of muscle tissues), and multi-organ failure.

High-risk groups include:

• People 65 years and older
• People of any age with chronic medical conditions like asthma, diabetes, or heart disease
• Pregnant people
• Children younger than 5 years and especially those younger than 2 years
  

Who Should Avoid the Flu Shot

As important as the flu shot is, it is not recommended for everyone. According to the CDC, flu vaccines should not be given to:

• Children under 6 months of age: This is because infants have immature immune systems and cannot respond to a flu vaccine.
• People with a prior severe allergic reaction to the flu shot or an allergy to an ingredient in any vaccine: If you have had such a reaction, you may not be able to receive any other form of flu vaccine. Speak with your healthcare provider.

The CDC previously recommended that people with egg allergies get their flu vaccine in an inpatient or outpatient setting, but they no longer recommend any additional safety measures for people with egg allergies, regardless of severity.

Some people with a history of a severe paralyzing illness called Guillain-Barré Syndrome (GBS) should also not get a flu vaccine. Talk to your healthcare provider before getting vaccinated if you have had GBS.

Summary

You don't need to postpone your flu shot for a mild illness. If you have a high fever or moderate to severe illness with or without a fever, however, delay vaccination until you've recovered. If in doubt, contact your healthcare provider.

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