A headache the day after a vaccination is usually a normal reaction to the vaccine. However, if the headache is severe or persists without relief, you should go to the hospital promptly. Vaccine is a heterologous protein, and while the body receives stimulation from foreign antigenic proteins, it may have an unfavorable immune response or allergic reaction to foreign proteins and vaccine adjuvants while obtaining a beneficial immune response and producing antibodies. Short ones can occur a few hours after vaccination, while long ones can occur 2-3 days after vaccination, so it is normal to have a headache the next day. Common adverse reactions after vaccination include: 1) systemic adverse reactions: such as low fever, headache, dizziness, chills, etc.; 2) local adverse reactions: such as redness, swelling, hard nodules, pain, itching, etc. at the injection site; 3) gastrointestinal adverse reactions: nausea, vomiting, loss of appetite, diarrhea, etc. Some allergic people may have allergic reactions, manifested as allergic urticaria or angioneurotic edema. Headache is one of the common adverse reactions to the vaccine, which usually recovers gradually within 1-2 and does not require special treatment. Patients can help relieve it by proper rest, light head rubbing or acupressure. Take care not to consume excessive spicy and irritating foods such as chili, raw onion, ginger and garlic, and avoid drinking alcohol as much as possible to prevent the headache from getting worse.