- People with known comorbidities (Diabetes, hypertension, heart diseases, chronic respiratory diseases like bronchiectasis, COPD etc) except those mentioned above in inclusion. - People who will have not received homologous vaccine two doses of BBIBP-CorV vaccine or those whose previous medical record of last 2 doses will be missing . - Difference between homologous vaccine and heterologous vaccine if less than 6 months - Pregnancy - History of flu or cough at that time - Medical history of COVID-19 at time of trial - On immunosuppressive therapy - Diagnosed with an immunocompromising condition

- People with known comorbidities (Diabetes, hypertension, heart diseases, chronic respiratory diseases like bronchiectasis, COPD etc) except those mentioned above in inclusion. - People who will have not received homologous vaccine two doses of BBIBP-CorV vaccine or those whose previous medical record of last 2 doses will be missing . - Difference between homologous vaccine and heterologous vaccine if less than 6 months - Pregnancy - History of flu or cough at that time - Medical history of COVID-19 at time of trial - On immunosuppressive therapy - Diagnosed with an immunocompromising condition