evidence: Reactions to a vaccine usually occur shortly after the vaccination and can last for several days. In the case of the COVID-19 vaccines, these can involve pain or tenderness at the injection site — in other words, a sore arm — or headaches. These symptoms show that the body's immune system is dealing with the vaccine. [...] In its safety report, the Paul Ehrlich Institute, a German federal health agency that regulates and researches vaccines and biomedicines, lists known, yet very rare, side effects of the COVID-19 vaccines. They include, for example, myocarditis, an inflammation of the heart muscle, and pericarditis, an inflammation of the pericardium, whereby the causal relationship has not yet been conclusively clarified in the cases reported to date. [...] Leading immunology experts in Germany largely rule out the possibility of people becoming ill years later as a result of COVID-19 vaccinations. The human body reacts to the vaccine immediately after receiving the shot or a few weeks later — and can then develop vaccine reactions or more severe symptoms.