* has a contraindication to bnt162b2, azd1222 or sinovac * has received an incomplete primary covid-19 vaccination series * has received 3 doses of covid-19 vaccine * has received heterologous primary covid-19 vaccination series * history of a solid organ or bone marrow transplant * history of malignancy (other than non-melanoma skin cancer) within the past five years * currently on hemodialysis * any confirmed or suspected immunosuppressive or immunodeficiency condition or diagnosis * on chronic (\>30 days) use of immunosuppressive medications at the time of enrollment (except topical steroids or short-term oral steroids, i.e., ≤14 days) * known diagnosis of hiv with cd4 count \<200 cells/mm3 (in the past 6 months) * active or history of previous auto-immune neurological disorders (e.g., multiple sclerosis, guillain-barre syndrome, transverse myelitis) (excluding bell's palsy) * has received anti-cd20 monoclonal antibodies for any reason in the past 12 months * has received monoclonal antibodies to treat a previous covid-19 event * pregnant at screening * positive sars-cov-2 antigen test in respiratory specimen at screening * planning to migrate out of the study area within 6 months of the enrollment * participants currently enrolled in any other covid-19 vaccine research trial in which they are getting a covid-19 vaccine during the study period * illiterate individuals (brazil only) * has a severe and/or uncontrolled comorbidity pakistan (natural infection priming group (priming group 3-p)): ● prior vaccination with any vaccine against covid-19

* has a contraindication to bnt162b2, azd1222 or sinovac * has received an incomplete primary covid-19 vaccination series * has received 3 doses of covid-19 vaccine * has received heterologous primary covid-19 vaccination series * history of a solid organ or bone marrow transplant * history of malignancy (other than non-melanoma skin cancer) within the past five years * currently on hemodialysis * any confirmed or suspected immunosuppressive or immunodeficiency condition or diagnosis * on chronic (\>30 days) use of immunosuppressive medications at the time of enrollment (except topical steroids or short-term oral steroids, i.e., ≤14 days) * known diagnosis of hiv with cd4 count \<200 cells/mm3 (in the past 6 months) * active or history of previous auto-immune neurological disorders (e.g., multiple sclerosis, guillain-barre syndrome, transverse myelitis) (excluding bell's palsy) * has received anti-cd20 monoclonal antibodies for any reason in the past 12 months * has received monoclonal antibodies to treat a previous covid-19 event * pregnant at screening * positive sars-cov-2 antigen test in respiratory specimen at screening * planning to migrate out of the study area within 6 months of the enrollment * participants currently enrolled in any other covid-19 vaccine research trial in which they are getting a covid-19 vaccine during the study period * illiterate individuals (brazil only) * has a severe and/or uncontrolled comorbidity pakistan (natural infection priming group (priming group 3-p)): ● prior vaccination with any vaccine against covid-19

has a contraindication to bnt162b2, azd1222 or sinovac has received an incomplete primary covid-19 vaccination series has received 3 doses of covid-19 vaccine has received heterologous primary covid-19 vaccination series history of a solid organ or bone marrow transplant history of malignancy (other than non-melanoma skin cancer) within the past five years currently on hemodialysis any confirmed or suspected immunosuppressive or immunodeficiency condition or diagnosis on chronic (>30 days) use of immunosuppressive medications at the time of enrollment (except topical steroids or short-term oral steroids, i.e., ≤14 days) known diagnosis of hiv with cd4 count <200 cells/mm3 (in the past 6 months) active or history of previous auto-immune neurological disorders (e.g., multiple sclerosis, guillain-barre syndrome, transverse myelitis) (excluding bell's palsy) has received anti-cd20 monoclonal antibodies for any reason in the past 12 months has received monoclonal antibodies to treat a previous covid-19 event pregnant at screening positive sars-cov-2 antigen test in respiratory specimen at screening planning to migrate out of the study area within 6 months of the enrollment participants currently enrolled in any other covid-19 vaccine research trial in which they are getting a covid-19 vaccine during the study period illiterate individuals (brazil only) has a severe and/or uncontrolled comorbidity pakistan (natural infection priming group (priming group 3-p)): ● prior vaccination with any vaccine against covid-19

has a contraindication to bnt162b2, azd1222 or sinovac has received an incomplete primary covid-19 vaccination series has received 3 doses of covid-19 vaccine has received heterologous primary covid-19 vaccination series history of a solid organ or bone marrow transplant history of malignancy (other than non-melanoma skin cancer) within the past five years currently on hemodialysis any confirmed or suspected immunosuppressive or immunodeficiency condition or diagnosis on chronic (>30 days) use of immunosuppressive medications at the time of enrollment (except topical steroids or short-term oral steroids, i.e., ≤14 days) known diagnosis of hiv with cd4 count <200 cells/mm3 (in the past 6 months) active or history of previous auto-immune neurological disorders (e.g., multiple sclerosis, guillain-barre syndrome, transverse myelitis) (excluding bell's palsy) has received anti-cd20 monoclonal antibodies for any reason in the past 12 months has received monoclonal antibodies to treat a previous covid-19 event pregnant at screening positive sars-cov-2 antigen test in respiratory specimen at screening planning to migrate out of the study area within 6 months of the enrollment participants currently enrolled in any other covid-19 vaccine research trial in which they are getting a covid-19 vaccine during the study period illiterate individuals (brazil only) has a severe and/or uncontrolled comorbidity pakistan (natural infection priming group (priming group 3-p)): ● prior vaccination with any vaccine against covid-19