Symptoms after vaccination typically appear very soon, mostly within the first 12 to 24 hours after the shot. Local reactions such as pain, swelling, or redness at the injection site usually start within 24 hours and last a few days. General symptoms like fever, tiredness, muscle aches, or headaches often begin around 24 hours after vaccination and typically resolve within a day or two. In some vaccines like MMR or chickenpox, fever and rash can begin later, usually between 1 and 4 weeks post-vaccination. Severe allergic reactions, although very rare, can start within minutes to a couple of hours after vaccination.
Local and General Symptoms Timing
- Local pain, swelling, and redness: within 12 to 24 hours, lasting 3 to 5 days.
- Fever and mild systemic symptoms: usually start within 24 hours, lasting 1 to 2 days.
- Some vaccines (e.g., MMR, chickenpox) may cause fever or rash starting 1 to 4 weeks later.
Severe Allergic Reactions
- Rare, occur within minutes up to 2 hours after vaccination.
- Immediate medical attention is needed if symptoms like breathing difficulty or swelling occur.
This timeline applies broadly to many common vaccines such as COVID-19, influenza, DTaP, MMR, and others.
