At the time of vaccination, vaccinees were instructed to report any adverse event to physicians or vaccination providers. Adverse events that were fatal or that resulted in disability and clusters of events (i.e., notably high numbers of similar adverse events related to a certain vaccine) were required to be reported within 2 hours after their occurrence. The following adverse events were required to be reported within 2 days after their occurrence: anaphylaxis or other allergic reactions occurring within 24 hours after vaccination; fever (axillary temperature, >37.5°C), angioedema, or a local injection-site reaction (diameter, >2.5 cm) occurring within 5 days after vaccination; purpura, an Arthus reaction, febrile convulsion, seizure, or polyneuritis occurring within 15 days after vaccination; and the Guillain-Barré syndrome occurring within 3 months after vaccination. Other reactions that were common and minor (e.g., mild pain and fatigue) were not required to be reported.