Combined Immunization of COVID-19 Inactivated Vaccine With QIV and PPV23

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