Reactions to the flu vaccine

With the arrival of the colder months, the circulation of respiratory viruses, such as Influenza — the cause of the flu — increases, as does the importance of vaccination. The flu vaccine is safe, effective, and remains the main strategy to reduce complications, hospitalizations, and deaths related to the infection.

According to pulmonologist and Sleep Medicine Specialist Jessica Polese, the flu is not just a simple viral infection. In some people, especially the elderly, pregnant women, children, and those with chronic illnesses, it can lead to severe cases. "The vaccine is a way to prevent this worsening and protect the entire community," she emphasizes. Many patients who have been vaccinated have questions about the side effects after the single application of the vaccine.

According to the doctor, it is common for some mild reactions to occur — a natural response of the body to the vaccine stimulus. "These reactions are not a cause for alarm. Most of the time, they are temporary and indicate that the immune system is being activated to form the desired protection," she explains.

Among the most reported effects in the first 24 to 48 hours after vaccination are:

1. Pain at the injection site – mild discomfort, redness. Cold compresses help relieve it.
2. Swelling – also common and temporary, can be reduced with cold compresses.
3. Headache – usually occurs between 6 and 12 hours after the application and improves spontaneously.
4. Muscle pain – generally in the arm, which may cause a feeling of heaviness or difficulty moving.
5. Mild fever (up to 38ºC) – may be accompanied by chills, fatigue, and sweating.
6. Red or purple spot on the arm – it is a benign effect and disappears naturally. Cold compresses help improve it.
7. Fatigue – a feeling of tiredness or mild discomfort that improves with rest and fluid intake.
8. Excessive sweating – may occur as a way for the body to regulate temperature.

The pulmonologist recommends resting on the day of the application and avoiding physical exertion. "If someone is doing any physical activity, for example, it's better to avoid it on that day," says Jessica.

And when should one seek help? "If there is very high fever, difficulty breathing, swelling of the lips or throat, rapid heartbeat, or symptoms of severe allergy, the patient should seek immediate medical assistance," she warns. But these are very rare cases.

Even with possible mild effects, Jessica states that the benefits of immunization far outweigh any temporary discomfort. "The vaccine saves lives and significantly reduces the burden of disease on healthcare services," she concludes.