Fig. 1: Trial profile.

This age-escalation phase 1 study was carried out in three stages. Seven days after the first dose of vaccination in each stage, total adverse events were collected and analyzed under blind status. If the incidence of adverse events of grade 3 or above does not exceed 15% of the total vaccinated participants, the enrollment of participants for the next stage could be initiated. ^*2 could not comply with follow-up; 2 had axillary temperatures of more than 37°C before vaccination; 5 excluded for abnormal laboratory test results; 1 had history of fever (≥38.0°C) within 3 days or acute illness requiring systemic antibiotic or antiviral therapy within 5 days; 1 had received a subunit or inactivated vaccine within 14 days; 19 were identified by the researchers as having potential medical or other issues that might influence the conduct of clinical research.