Preliminary Safety Assessment of a Quadrivalent Subunit Influenza Vaccine in China

This is an open-label, single-arm, non-controlled, real-world safety study of the quadrivalent subunit influenza vaccine, designed to systematically track and evaluate the overall safety profile following vaccine administration.

The core objectives of this study are as follows:

1. To assess the occurrence of rare adverse reactions with an incidence rate of less than 0.01% after vaccination;
2. To investigate the incidence of cerebral infarction events following receipt of the study vaccine;
3. To evaluate the incidence of systemic adverse events after vaccination among participants aged 9 to 17 years.

A total of 3,105 eligible participants aged 3 years and older who voluntarily receive the vaccine will be enrolled. All enrolled participants will be administered a single 0.5 mL intramuscular dose of the quadrivalent influenza subunit vaccine.

The safety monitoring protocol is arranged as follows:

1. 30-minute immediate observation: On-site monitoring will be conducted at the vaccination clinic immediately after injection to detect immediate adverse reactions.
2. 28-day systematic safety follow-up: Participants will perform daily self-monitoring of adverse events within 28 days after vaccination. Investigators will conduct two on-site centralized follow-up visits on Day 7 and Day 28 post-vaccination respectively, to verify and collect adverse event data.
3. 6-month serious adverse event monitoring: The occurrence of serious adverse events will be monitored via spontaneous reporting by participants within 6 months after vaccination.