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Vaccine Safety Center

Information on adverse events, contraindications, and reporting

Common Side Effects

Most vaccine side effects are mild, temporary, and a sign that the body is building immunity.

  • Local reactions: Pain, swelling, or redness at the injection site (very common).
  • Systemic reactions: Low-grade fever, fatigue, headache, muscle/joint pain, or chills.
  • Duration: Typically start within 24 hours and resolve in 1-3 days.

Serious Adverse Events

Severe adverse events are extremely rare but require immediate medical attention.

  • Anaphylaxis: Severe allergic reaction (approx. 1 in 1 million doses). Occurs within minutes to hours.
  • Guillain-Barré Syndrome (GBS): Very rare neurological complication associated with some vaccines.
  • Syncope: Fainting, most common in adolescents (e.g., HPV vaccine). Observe for 15 mins post-vaccination.

True Contraindications

Conditions where a vaccine should absolutely NOT be given:

  • Severe allergic reaction (anaphylaxis) to a previous dose or to a vaccine component.
  • For Live Vaccines (MMR, Varicella, Yellow Fever): Severe immunodeficiency, pregnancy.
  • Encephalopathy within 7 days of a previous pertussis-containing vaccine.

Reporting & Monitoring

Vaccine safety is continuously monitored globally through rigorous reporting systems.

  • VAERS (US): Vaccine Adverse Event Reporting System. Anyone can submit a report.
  • VSD (US): Vaccine Safety Datalink for active surveillance.
  • Cold Chain: Vaccines must be stored strictly between 2°C and 8°C (for refrigerated) to maintain safety and efficacy.