Both CDC and FDA review data reported to Vaccine Adverse Event Reporting System, or VAERS. FDA reviews reports to assess whether a reported event is adequately reflected in product labeling, and closely monitors reporting trends for individual vaccine lots. Approximately 85% of the reports describe mild events such as fever, local reactions, episodes of crying or mild irritability, and other less serious experiences. The remaining 15% of the reports reflect serious adverse events involving life-threatening conditions, hospitalization, permanent disability, or death, which may or may not have been truly caused by an immunization. | 
