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The most common reactions to the flu vaccine include pain, redness, or swelling at the injection site, as well as fever, muscle pain, and headache, which usually occur within a few hours of receiving the vaccine.
These reactions are mild and usually improve in 2 to 3 days, without needing any specific treatment. Even so, there are some precautions that allow alleviating each type of reaction caused by the vaccine.
However, some more serious reactions such as allergy, high fever, rapid heartbeat, shortness of breath, weakness or paralysis in the body may also appear. In these cases, it is important to seek medical help.
The most common reactions that can be caused by the flu vaccine are:
1. Pain at the application site
One of the most common adverse reactions that can occur with the administration of the flu vaccine is reactions at the injection site, such as pain, redness or swelling at the injection site. This reaction can occur up to 72 hours after vaccination and is usually more common in people over 65.
How to relieve: a cold compress should be applied to the arm where the vaccine was applied, within the first 24 to 48 hours after vaccination. If the pain is very severe, the redness is in a large area on the arm or the person has difficulty moving the arm, you should go to the doctor immediately.
2. Headache or muscle pain
Headache or muscle pain may appear about 6 to 12 hours after vaccination and usually improve within two days. In addition, some people may also experience joint pain.
How to relieve: rest and drink plenty of fluids. If the pain is severe, you can take analgesics prescribed by the doctor, such as paracetamol or dipyrone, for example.
Another common side effect of the flu vaccine is a mild fever of up to 38ºC, considered normal after vaccination, and which can be accompanied by chills, tiredness and excessive sweating, but these are usually transient symptoms that arise 6 to 12 hours after vaccination, and disappear in about 2 days.
How to relieve: you should drink plenty of fluids to keep your body hydrated, stay at rest and, if these symptoms cause a lot of discomfort, you can take analgesics and antipyretics, with medical indication, such as paracetamol or dipyrone, for example.
Although it is very rare, the flu shot can also give rise to more serious reactions that need immediate medical attention, such as:
- Very high fever, above 39ºC;
- Itching, hives or skin lesions that can occur all over the body;
- Severe allergic reactions or anaphylactic shock, may appear at the time or a few hours after the vaccine is given with symptoms of rapid heartbeat, shortness of breath, swelling of the lips, tongue or throat, dizziness or even cardiac arrest. See other symptoms of anaphylactic shock;
- Guillain-Barré syndrome, with symptoms of weakness and paralysis throughout the body and can develop in people who have had the syndrome in the past, it is important to inform the doctor who has already had Guillain-Barré Syndrome so that the person can be evaluated as to whether or not the person should be vaccinated. Learn more about Guillain-Barré syndrome;
- Inflammation of blood vessels, including those present in the kidneys, lungs and heart, which can cause symptoms of malaise, tiredness, fever, loss of appetite and weight loss;
- Swelling of the glands in the neck, armpit, or groin, due to changes in the lymphatic system that can cause bumps.
When any of these serious reactions are suspected, it is important to seek immediate medical help or the nearest emergency room.