Why do the side effects even occur?
According to Professor Robert Read, head of clinical and experimental sciences, the sore arm can be because of the trauma of the needle in the muscle or inflammation in the muscle, probably due to the chemicals in the injection.
Most of the time, this sounds scarier than it really is. For a sore arm, it’s recommended to ice it down. And the pain or soreness should subside in roughly twenty-four hours.
Any other common side effects, including muscle aches, flu-like symptoms, and fatigue, are likely due to the generalized activation of the immune system induced by the vaccine.