History of allergic reactions after receiving any previous Covid-19 vaccines or any other drug or vaccine Having any acute or chronic illness requiring continuous ongoing medical or surgical care within the last months History of severe cardiovascular disease such as heart failure, or hospitalization due to heart disease within the last year Pregnancy declared by the participant based on the first day of the last menstrual period (LMP) Breastfeeding History of receiving any vaccine within 14 days of receiving the intranasal booster dose Received blood and/or any blood products and/or immunoglobulins within three months prior to the intranasal booster dose Diagnosed (suspected or confirmed) with immunocompromising illneses, history of long-term use of immunosuppressive drugs, including history of long-term use of systemic corticosteroids equivalent to 10 mg or more daily prednisolone for more than 14 consecutive days with the exception of topical steroids within the last 4 months Recent diagnosis or treatment of cancers except basal cell carcinoma and In-situ cervical cancer History of uncontrolled serious psychiatric illnesses History of blood disorders (dyscrasia, coagulopathy, platelet deficiency or disorder, or deficiency of blood clotting factors) History of chronic neurological diseases (including seizures and epilepsy) Current substance or alcohol abuse Acute febrile illness at the time of receiving the booster dose Splenectomy for any reason Close contact with a confirmed COVID-19 case within two weeks before participating in the current study Continued use of anticoagulants such as coumarin and related anticoagulants (such as warfarin) or new oral anticoagulants / antiplatelet agents. Note: Less than 325 mg of aspirin per day as prophylaxis is allowed Chronic unstable diseases in the last 4 weeks, including hospitalization due to surgery, deterioration of one of the organ system's function, a need to add new drugs or serious dose adjustments for existing drugs

History of allergic reactions after receiving any previous Covid-19 vaccines or any other drug or vaccine Having any acute or chronic illness requiring continuous ongoing medical or surgical care within the last months History of severe cardiovascular disease such as heart failure, or hospitalization due to heart disease within the last year Pregnancy declared by the participant based on the first day of the last menstrual period (LMP) Breastfeeding History of receiving any vaccine within 14 days of receiving the intranasal booster dose Received blood and/or any blood products and/or immunoglobulins within three months prior to the intranasal booster dose Diagnosed (suspected or confirmed) with immunocompromising illneses, history of long-term use of immunosuppressive drugs, including history of long-term use of systemic corticosteroids equivalent to 10 mg or more daily prednisolone for more than 14 consecutive days with the exception of topical steroids within the last 4 months Recent diagnosis or treatment of cancers except basal cell carcinoma and In-situ cervical cancer History of uncontrolled serious psychiatric illnesses History of blood disorders (dyscrasia, coagulopathy, platelet deficiency or disorder, or deficiency of blood clotting factors) History of chronic neurological diseases (including seizures and epilepsy) Current substance or alcohol abuse Acute febrile illness at the time of receiving the booster dose Splenectomy for any reason Close contact with a confirmed COVID-19 case within two weeks before participating in the current study Continued use of anticoagulants such as coumarin and related anticoagulants (such as warfarin) or new oral anticoagulants / antiplatelet agents. Note: Less than 325 mg of aspirin per day as prophylaxis is allowed Chronic unstable diseases in the last 4 weeks, including hospitalization due to surgery, deterioration of one of the organ system's function, a need to add new drugs or serious dose adjustments for existing drugs