- acute severe illness - recent receipt of a blood product - history of thrombocytopenia - pregnant females - any chronic medical condition - any participant receiving any immune suppressive medication - immunocompromised staff - participants who have egg allergy - participants who care for immune compromised hosts - participants who test positive for covid-19 serology prior to randomization

- acute severe illness - recent receipt of a blood product - history of thrombocytopenia - pregnant females - any chronic medical condition - any participant receiving any immune suppressive medication - immunocompromised staff - participants who have egg allergy - participants who care for immune compromised hosts - participants who test positive for covid-19 serology prior to randomization