Common vaccine side effects reflect the immune system responding as intended: soreness or swelling at the injection site, fatigue, headache, mild fever, or aching muscles for a day or two. These usually settle on their own, and simple measures like rest and fluids help. A pharmacist can advise on relief such as paracetamol if needed.
Serious allergic reactions are extremely rare, which is why vaccination is usually followed by a short observation period so staff can respond immediately if needed. The overall safety of licensed vaccines is monitored continuously after approval.
Seek urgent care if you develop signs of a severe allergic reaction shortly after a vaccine, such as difficulty breathing, swelling of the face or throat, or a widespread rash, and call your local emergency number. Tell a clinician about any past reaction so they can advise on future doses. For nearly everyone, the protection vaccines provide far outweighs these small risks.