The most common reactions to the flu shot include pain, redness, or swelling at the injection site. You may also experience a fever, muscle aches, and a headache shortly after receiving the vaccine.
Most of these side effects are mild and typically resolve on their own within two to three days. You usually do not need specific medical treatment, but simple home care can help manage your discomfort.
If your symptoms do not improve or if they begin to worsen, you should consult a doctor or a pediatrician. Seeking professional advice ensures that any unusual reactions are monitored and managed correctly.
Main flu shot side effects
The most common side effects associated with the influenza vaccine include:
1. Injection site pain
One of the most frequent adverse reactions to the flu shot is discomfort where the needle entered the skin. You may notice pain, redness, or even the development of a small, hard lump at the site.
These localized reactions can appear up to 72 hours after vaccination. They are statistically more common in adults over the age of 65.
What to do: Apply a cold compress to the area for 10 to 15 minutes at a time during the first 48 hours. If the pain is severe, the redness spreads significantly, or you cannot move your arm, seek medical attention immediately.
2. Swelling at the injection site
Swelling around the area where you received the shot is a normal response that may develop within 72 hours. This typically subsides on its own as your body processes the vaccine.
What to do: While the swelling will naturally decrease over a few days, applying a cold compress can help speed up the process and provide relief.
3. Headache
A headache may develop roughly 6 to 12 hours after your appointment. In most cases, this side effect clears up within 48 hours.
What to do: Prioritize rest and stay well hydrated by drinking plenty of water. If the headache is bothersome, you can take an over the counter pain reliever like acetaminophen.
4. Muscle aches
Some people experience body aches or muscle soreness 6 to 12 hours after getting the flu shot. You might feel like your arm is heavy or find it slightly difficult to move comfortably.
What to do: Muscle soreness usually fades within two days. If you need relief, your doctor may recommend an over the counter anti inflammatory medication.
5. Fever
A low grade fever (up to 100.4°F) is considered a normal immune response to the vaccine. This may be accompanied by chills, fatigue, or sweating, but these symptoms are usually temporary and disappear within two days.
What to do: Drink plenty of fluids to stay hydrated and get adequate rest. If the fever causes significant discomfort, you can use over the counter fever reducers like acetaminophen, following the dosage on the label or your doctor's advice.
6. Red or bruised spots
You may notice a red, purple, or bluish spot, known as ecchymosis, near the injection site during the first two days. This is essentially a small bruise caused by the needle.
What to do: You can apply a cold compress to the area during the first 48 hours. Wrap ice or a cold pack in a clean cloth or towel and apply it to the arm for 10 to 15 minutes, up to three times a day.
7. Fatigue
Feeling tired or generally under the weather is a common side effect within the first 48 hours of vaccination. This is a sign that your immune system is working to build protection.
What to do: It is best to rest and avoid strenuous activities, such as intense gym workouts, for a day or two. Increasing your fluid intake can also help your body recover more quickly.
8. Sweating
Increased sweating can occur in the first 48 hours as your immune system responds to the vaccine. This is often the body’s way of regulating its internal temperature, especially if a mild fever is present.
What to do: Stay hydrated, rest, and wear lightweight clothing to stay cool. If the sweating is related to a fever, a lukewarm bath or a cool damp cloth on the forehead may provide relief.
Rare flu shot side effects
While extremely rare, some people may experience serious reactions that require immediate medical intervention:
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High fever (above 102.2°F).
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Intense itching, hives, or skin rashes that spread across the body.
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Severe allergic reactions or anaphylaxis, which may cause a rapid heartbeat, difficulty breathing, or swelling of the lips and throat.
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Guillain-Barré Syndrome, characterized by weakness or tingling that can lead to paralysis. If you have a history of this syndrome, consult your doctor before getting vaccinated.
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Vasculitis (inflammation of the blood vessels), which may cause fatigue, loss of appetite, and weight loss.
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Swollen lymph nodes in the neck, armpit, or groin.
If you suspect you are having a severe reaction, call 911 or go to the nearest emergency room immediately.