Flu, Covid-19, gastroenteritis… To protect themselves from the nasty winter viruses, many French people resort to vaccination. But once the product is injected, some people look grim: they complain of arm pain, fever, intense fatigue or even body aches. How can we explain then that some react to the vaccine while others feel absolutely nothing? And what is happening in our body for such a cascade of reactions to occur? Dr Gérald Kierzek, emergency doctor and medical director of True Medical, guides us.
What happens to your body during vaccination
What happens in our body after the injection? In reality, the vaccine acts as a simulacrum of infection, admits the medical director of True Medical.
“Vaccines introduce an antigen (i.e. the harmless part of a virus or bacteria) which mimics an infection, prompting immune cells to produce antibodies and memory cells. This response causes local or general inflammation, hence effects such as fever or body aches, which disappear within 1 to 3 days,” he explains to us.
In summary, therefore, the vaccine introduces into the body a harmless version of the virus or bacteria, close enough to the original for the immune system to recognize it, but without causing disease.
“The body responds to vaccines because they stimulate the immune system to produce a protective response against specific pathogens,” says the doctor again, before specifying that the appearance of side effects is completely normal. “Symptoms such as arm pain, fatigue or fever reflect this immune activation.”
But if these elements constitute the beginning of a response, how can we explain why some people do not feel this immune stimulation? In reality, the absence of symptoms is quite common… and appears to be multifactorial.
Why do side effects vary for each individual?
According to the medical director of True Medical, the absence of symptoms should not worry you: this does not mean that the vaccine did not work. You are just lucky.
“The effects differ depending on age, sex, genetic polymorphism, health status (for example, obesity promotes chronic inflammation) and prior experience with the antigen. A strong reaction also often indicates a very reactive immune system, but the absence of symptoms in no way means that it is a vaccine failure,”
he says.
The way your body reacts to the same vaccine may differ. It depends on your energy level at the time of the injection, the precise formulation of the vaccine and your immune memory.
Can we avoid these inconveniences?
No, it is not possible to anticipate their appearance. On the other hand, you can try to alleviate certain symptoms linked to an injection by taking paracetamol for prevention.
“Taking paracetamol before or after the injection helps reduce fever and pain. However, never exceed the recommended dose. Also remember to hydrate, rest and avoid intense exercise. Finally, consult a doctor if symptoms persist beyond 48 hours or worsen,” concludes the medical director of True Medical.