Vaccine side effects, such as headache, rupture, or fever, are signs of an immune system reaction and are commonly encountered during immunizations.

"One day after vaccination you should not plan strenuous physical activity," says Dr. Peter Marks, chief of vaccines at the US Food and Drug Administration, says he himself felt a break after taking the first dose.

Here's what happens: The immune system works in two ways, one activating the moment the body detects a foreign object in the body. White blood cells are mobilized in that part of the body where the "enemy" has intervened, causing swelling, which is also accompanied by fever, localized pain and rupture.

This rapid response of the immune system weakens over the years. For this reason young people feel stronger side effects than adults. Also, some vaccines cause a stronger reaction.

But everyone reacts differently. If you do not feel any side effects a day or two after vaccination, do not assume that the vaccine is not working.

Even without being felt, vaccines activate the second track of the immune system, which offers real protection by producing antibodies.

Another annoying side effect is observed when the lymph nodes, such as the glands under the arms, become swollen. Women are advised to have a mammogram before the COVID vaccine so that the swollen glands are not misdiagnosed as cancer.

Not all side effects are normal. After administering hundreds of millions of doses worldwide and following closely the response of those vaccinated, a small percentage of those who received the AstraZeneca or Johnson & Johnson vaccine reported blood clots. But health officials say the benefits of the vaccine far outweigh the risks.

Some individuals have experienced severe allergic reaction. Therefore, after vaccination, everyone should wait in the clinic for 15 minutes to guarantee that they will not have a reaction.

Authorities are trying to find out if temporary swelling of the heart tissue that occurs during certain forms of infection may be a side effect of vaccines that use the RNA genetic code, such as Pfizer and Moderna. US health officials still do not know if there is a connection between them, so they are following the data, especially for the reaction of teenagers and young people./VOA