Why you shouldn't get a flu shot if you have a fever

• You can get a flu shot with a cold as long as you don't have a fever over 99.5°F.
• You also shouldn't get a flu shot if you're having trouble breathing.
• Getting a flu shot with a cold will not make any potential side effects of the flu shot worse.

Around 200,000 people in the US are hospitalized each year with complications from the flu - a respiratory infection caused by the influenza virus. And though the best way to prevent the flu is by getting a flu shot, you should wait to get vaccinated if you have severe symptoms of another illness.

Can you get a flu shot with a cold?

It's generally safe to get a flu shot with a cold or other mild illness.

"In most cases, a cold will not inhibit your body's expected immune response to the vaccine," says Stephen Cobb, MD, a family medicine doctor and physician executive at Centura Health in Colorado.

This means that the flu shot will be just as effective and you aren't likely to have extra side effects if you get vaccinated while you have a cold.

You can also get the flu shot if you have other mild conditions, like a sinus infection or seasonal allergies.

Don't get the flu shot with a fever

While it's generally okay to get the flu shot with a cold or other mild illness, you should wait to get vaccinated if you have a fever of over 99.5°F or signs of respiratory distress like shortness of breath and chest discomfort.

If you have either of these symptoms, it indicates the possibility of a more severe illness that may be exacerbated by the side effects of a flu shot, says Charles Bailey, MD, the medical director for infection prevention at Mission Hospital and St. Joseph Hospital in Orange County, California.

In addition, the flu shot may not be as effective if you get it while sick with another severe illness because your immune system is already working over time. Since flu shots work by prompting your body to produce antibodies, you might not get the full effect of the vaccine if your immune system is already working to help you recover from a serious illness.

Another reason to avoid the flu shot if you have a fever is that it may mask the signs if you have an allergic reaction to the vaccine.

Most allergic reactions occur within the first hour of getting a vaccine and include symptoms like a high fever, nausea, and muscle aches. If you already have a fever, it could be difficult to know if you're having an allergic reaction, or not.

Insider's takeaway

It's usually safe to get a flu shot if you have a cold or any mild illness. Still, you should wait a few days or talk to your doctor before getting a flu vaccine if you have a fever or other severe symptoms.

The seasonal flu shot is effective in preventing over 4 million infections. It's important to get one every year to protect both yourself and others from the highly contagious flu virus and potential complications.

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