Can I Get a Flu Shot While Sick?

You can still get a flu shot if you have a cold if your symptoms are mild. This includes people with mild sniffles and no fever. 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.

This article describes when you should delay getting the flu shot and when you shouldn't. It also explains why delaying the shot can put your health at risk and why certain groups need to avoid it entirely.

reasons not to get a flu shot when you're sick

Verywell / Cindy Chung

How the Flu Shot Works

Vaccines are designed to stimulate a protective immune response. With the flu shot, it does so with influenza (flu) viruses that have been killed. These are called inactivated vaccines.

Once these dead viruses have been injected into your body, your immune system will respond as if the viruses are alive and produce Y-shaped proteins called antibodies. These antibodies are tailor-made to recognize and defend against the specific viruses you were injected with.

So, if you do happen to get the flu, the antibodies will be on hand to launch an immediate attack, preventing infection or at the very least making it less severe.

But the antibody defense is short-lived and gradually wanes over time. This is why you need to get a flu shot every year—to not only "up" your immune defenses but to also immunize you against the specific flu strains that are predicted to circulate in the coming flu season.

How Sickness Affects the Flu Shot

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

Being moderately or severely ill also weakens the immune system, albeit temporarily. If you're sick when you get the flu shot, your immune system is already hard at work fighting the other illness or infection. This means it may not have the resources to produce enough antibodies to afford immune protection.

This is especially true in older adults whose immune response tends to weaken over time. (This also accounts for why high-dose flu vaccines are recommended for adults over 65.)

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

When It's OK to 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, or cough
  • An ear infection (otitis media)
  • Mild diarrhea

What Is the Best Time for the Shot?

To better ensure protection throughout the entire flu season, get the flu shot or nasal flu spray (FluMist) in September or October.

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 reasons for postponing the flu shot is a moderate to high fever. In adults, this is generally when a temperature 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 Flu Shots Most

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 Needs to 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 doctor if you have had GBS before getting vaccinated.

Summary

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

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10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Kristina Herndon, RN
Kristina Herndon, BSN, RN, CPN, has been working in healthcare since 2002. She specializes in pediatrics and disease and infection prevention.