What are the side effects of vaccines?
Mar 21, 2025
Source: Cainiu Health
Dr. Yang Ziqi
Introduction
In general, vaccines are biological products made from various pathogenic microorganisms and are used for preventive vaccination. Possible side effects of vaccines may include local redness, swelling and pain, fever, rash, gastrointestinal reactions, headache, and dizziness. Vaccine side effects are diverse, but most are mild and tolerable. Before receiving a vaccination, it is important to fully understand the vaccine information.
Generally speaking, vaccines are biological products made from various pathogenic microorganisms used for preventive vaccination. Possible side effects of vaccines include local redness, swelling, pain, fever, rash, gastrointestinal reactions, headache, and dizziness. A detailed analysis is as follows:
1. Local redness, swelling, and pain
The antigen components in the vaccine stimulate immune cells at the injection site, triggering an immune response that causes local vasodilation and plasma exudation, leading to redness and swelling. Meanwhile, inflammatory mediators released during the immune response, such as prostaglandins, stimulate nerve endings, producing a sensation of pain.
2. Fever
As a foreign antigen, the vaccine entering the body activates the immune system, causing immune cells to release cytokines such as interleukins. These cytokines act on the hypothalamic thermoregulatory center, raising its set point, which increases heat production and decreases heat dissipation, thereby causing fever.
3. Rash
Components of the vaccine may trigger allergic reactions in the body. The immune system identifies certain substances in the vaccine as foreign allergens, producing antibodies and releasing allergy-related mediators such as histamine. Histamine causes skin vasodilation and increased vascular permeability, leading to rashes and accompanying skin itching.
4. Gastrointestinal reactions
The systemic immune response triggered by vaccination may affect the gastrointestinal tract, disrupting its normal motility and secretion rhythm of digestive fluids. Cytokines released by the immune system may also influence the neural regulatory function of the gastrointestinal tract, resulting in symptoms such as nausea, vomiting, and diarrhea.
5. Headache and dizziness
Following vaccination, the activated immune system releases inflammatory mediators and cytokines into the bloodstream, which may affect the vasomotor function of cerebral blood vessels. Abnormal states of cerebral vessels can alter cerebral blood perfusion and stimulate nerves, thereby causing discomfort such as headache and dizziness.
Vaccine side effects are diverse, but most are mild and tolerable. Before vaccination, it is important to fully understand vaccine information and the recipient's health status to prevent or reduce the occurrence of side effects. If severe side effects occur, timely medical attention should be sought.
