The main objective of this study was to evaluate the immunogenicity and safety of the booster dose of COVID-19 inactivated vaccine and co-immunization with quadrivalent influenza vaccine and 23-valent pneumonia polysaccharide vaccine in people aged 18 years and older. A randomized controlled, open trial design was adopted.

The study was conducted with informed consent of the subjects for immunogenicity and safety in the population aged 18 years and older. A total of 3000 healthy subjects were selected, (1)600 healthy subjects were selected for the immunogenicity and safety study of co-immunization, 300 in the adult group (18-59 years old) and 300 in the elderly group (60 years old and above); (2) 2400 healthy subjects were selected for the observational study of the safety of co-immunization, 1200 in the adult group (18-59 years old) and 1200 in the elderly group (60 years old and above ) 1200 people.

Inclusion Criteria:

• Healthy adults 18 years old and older
• Over 6 months after primary immunization with COVID-19 vaccines
• Can understand and sign the consent
• Can provide effective personal identification

Exclusion Criteria:

• Has a history of COVID-19 infection
• Less than 6 months after primary immunization with COVID-19 vaccines
• Already vaccinated with influenza vaccines of that year
• Vaccinated with pneumococcal vaccines within 5 years
• Has a history of severe hypersensitivity reaction to vaccines
• Has uncontrolled seizure or other severe neural system illnesses
• Has a fever, chronic disease, or acute disease during immunization
• Gestation period, lactation period, or planning to get pregnant within 3 months
• Administrated with other drugs under research within 30 days before vaccination
• Received attenuated vaccines within 14 days before vaccination
• Received subunit vaccines or inactivated vaccines within 7 days before vaccination
• Other conditions based on researcher's judgement