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- Flu shot side effects can include soreness at the injection site, headache, and a mild fever.
- The side effects of the nasal spray are runny nose, wheezing, sore throat, headaches, and fever.
- Allergic reactions are about one in a million, but trouble breathing could indicate one.
- Visit Insider's Health Reference library for more advice.
The flu shot has some side effects like soreness around the injection site and headaches, but these are short-lived and should not deter you from getting vaccinated.
On rare occasions, the flu shot could trigger an allergic reaction that needs to be treated by a doctor.
Here's what you need to know about the side effects of the flu shot and how to tell the difference between a normal response and an allergic reaction.
Common side effects of the flu shot
Some of the most common side effects of the flu vaccine include:
- Soreness, redness, a small rash, or swelling at the site of injection
- Headache
- Mild fever (less than 101 °F)
- Nausea or stomach pain
Side effects typically begin shortly after injection and should only last a few days, according to the CDC.
"Headache, fever, and sore muscles are not a sign of allergic reactions," says Michael McNeil, MD MPH, Team Lead for Vaccine Safety Datalink at the CDC's Immunization Safety Office. "These reactions can occur as a result of the patient's immune system responding to a vaccine."
Most of these side effects are unavoidable, but to avoid arm soreness, try taking ibuprofen two hours before you receive your vaccination.
Side effects of the nasal spray
Getting a nasal spray flu vaccine may help you avoid some side effects of the flu shot, like arm soreness, but it comes with its own share of side effects.
Possible side effects from the nasal spray vaccine include:
- Runny nose
- Wheezing
- Sore throat
- Headaches
- Fever
- Nausea
Nasal vaccines are safe for most individuals between the age of 2 and 49, according to the CDC. But some groups who should not get the nasal spray include:
- People with a weakened immune system
- Adults who are 50 or older
- Children ages 2-4 who have had severe asthma within the past year
- Children ages 2-17 who are taking medications such as aspirin and salicylate-containing therapies
- Pregnant women
In addition, those who should exercise an abundance of caution when receiving the nasal spray vaccine include:
- People over 5 with asthma
- People with lung disease, heart disease, or diabetes
- People who currently have an acute illness
Find a complete list of who should avoid the nasal spray and who should take precautions on the CDC's website.
Allergic reactions to the flu shot
Though the side effects listed above are normal reactions to the flu vaccine, it's important to monitor your response to the vaccine to make sure that you are not having an allergic reaction.
Though allergic reactions are rare - they occur in an estimated 1.3 of every 1 million vaccinations - they can be serious.
Symptoms of a serious allergic reaction to a flu vaccine include:
- Trouble breathing
- Hoarseness or wheezing
- Pallor/paleness
- Weakness
- Fast heartbeat
- Dizziness
According to McNeil, these symptoms usually occur "within a few minutes to a few hours after receiving the shot and they require immediate medical evaluation and treatment."
The flu shot, like all vaccines, contains several components that can cause an allergic reaction. Most allergic reactions are caused by an allergy to egg protein, gelatin, or other additives in the vaccine. While the flu shot contains trace amounts of egg, research has shown that most people with mild egg allergies can receive influenza vaccines.
Serious non-allergic reactions
In extremely rare cases, the influenza vaccine can trigger Guillain-Barré syndrome (GBS), a neurological disorder that causes paralysis.
It is estimated that only one-or-two individuals develop GBS for every 1 million people vaccinated. GBS can occur days or weeks after a vaccination, and is experienced as an acute muscle weakness, difficulty controlling eye muscles, or difficulty swallowing.
Anyone presenting these symptoms should contact their doctor.
Insider's takeaway
The flu vaccine - as a shot or nasal spray - can come with side effects including headache, fever, and nausea. However, it's still important to get vaccinated each year.
"Flu vaccines have a good safety record," says McNeil "Hundreds of millions of Americans have safely received flu vaccines over the past 50 years, and there has been extensive research supporting the safety of flu vaccines."
Influenza is a dangerous disease, particularly for the young, the elderly, and those with compromised immune systems.
Getting a flu shot will reduce your chance of catching the disease yourself, or passing it to those that are vulnerable. While there are potential side effects, they are minor and short-lived for most people and should not influence your plans to get a flu shot.