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 appear within a few hours after receiving the vaccine.
These reactions are mild and usually improve within 2 to 3 days, without requiring any specific treatment. Even so, there are some precautions that allow you to alleviate each type of reaction caused by the vaccine and, if symptoms do not improve or symptoms worsen, you should consult your general practitioner or pediatrician.
Read too: Flu vaccine: when to take it and side effects
In addition, some more serious reactions may also appear, such as allergies, high fever, rapid heartbeat, shortness of breath, weakness or paralysis in the body. In these cases, it is important to seek medical help immediately.
Main reactions to the flu vaccine
The most common reactions that can be caused by the flu vaccine are:
1. Injection site pain
One of the most common adverse reactions that can occur with the administration of the flu vaccine are reactions at the site of vaccine administration, such as pain and redness at the application site, or even the formation of a hard lump.
This reaction can occur up to 72 hours after vaccination and is generally more common in people over 65 years of age.
What to do: a cold compress should be applied to the arm where the vaccine was administered, 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 their arm, they should see a doctor immediately.
2. Swelling at the application site
Swelling at the flu vaccine injection site is a common reaction and can occur up to 72 hours after the vaccine, improving over time.
What to do: The swelling in the region improves over the days, and a cold compress can be applied to the area to help it go down faster.
3. Headache
The headache may appear about 6 to 12 hours after vaccination and usually improves within two days.
What to do: you should rest and drink lots of fluids. If the pain is severe, you can take painkillers recommended by your doctor, such as paracetamol or dipyrone, for example.
4. Muscle pain
Muscle pain may occur in some people after receiving the flu vaccine, and may occur between 6 and 12 hours after application. In some cases, the person may also feel the arm heavier and have greater difficulty moving it.
What to do: Muscle pain usually improves in about 2 days, however, to alleviate the pain, the doctor may recommend the use of anti-inflammatory drugs.
5. Fever
Another common side effect of the flu vaccine is a mild fever of up to 38ºC, considered normal after vaccination, and which may be accompanied by chills, tiredness and excessive sweat production, but are generally transient symptoms, which appear 6 to 12 hours after vaccination, and disappear in about 2 days.
What to do: You should drink plenty of fluids to keep your body hydrated, rest and, if these symptoms cause a lot of discomfort, you can take painkillers and antipyretics, with medical advice, such as paracetamol or dipyrone, for example.
6. Red spot
The red, purple or blue spot, called bruising, is another common side effect of the flu vaccine that can happen in the first 1 or 2 days on the arm where the injection was given.
What to do: a cold compress can be applied to the area within the first 24 to 48 hours after vaccination. To make a cold compress, you must place ice in a bag or ice pack, cover it with a clean cloth, towel or diaper and apply it to your arm for about 10 to 15 minutes, 3 times a day.
7. Fatigue
In the first 24 to 48 years after receiving the flu vaccine, tiredness or malaise may also appear as a common side effect.
What to do: It is recommended to rest and avoid vigorous activities, such as vigorous physical exercise, for example. Furthermore, it is important to increase your fluid intake to keep your body hydrated, facilitating recovery.
8. Sweating
Sweating is also a common reaction to the flu vaccine in the first 24 to 48 hours that can happen due to the immune system’s response to the vaccine or as the body’s way of regulating its temperature, especially in the case of a fever.
What to do: drinking plenty of water, resting and removing excess clothing can help reduce excessive sweating. Furthermore, if it was caused by a fever, some ways to reduce the fever are to take a warm bath or apply a cold towel to the forehead. See other ways to lower your fever.
Read too: How to alleviate the most common vaccine reactions
Rare flu vaccine reactions
Although very rare, the flu vaccine can also give rise to more serious reactions that need immediate medical attention, such as:
- Very high feverabove 39ºC;
- Itching, hives or skin lesions which can occur throughout the body;
- Severe allergic reactions or anaphylactic shock, may appear at the moment or a few hours after receiving the vaccine 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 Barre syndrome, with symptoms of weakness and paralysis throughout the body and can develop in people who have had the syndrome in the past, and it is important to inform the doctor that you have had Guillain-Barré Syndrome so that they can assess whether or not the person should be vaccinated. Learn more about Guillain-Barré syndrome;
- Inflammation of blood vesselsincluding those present in the kidneys, lungs and heart, which can cause symptoms of malaise, tiredness, fever, loss of appetite and weight loss;
- Swelling of glands in the neck, armpit or groindue to changes in the lymphatic system that can cause waterlogging.
When any of these serious reactions are suspected, it is important to seek medical help immediately or the nearest emergency room.
