Live attenuated viruses for protection against the novel coronavirus Sars-CoV-2 are provided. The live attenuated chimeric virus strains are based on a live attenuated influenza A or B virus (LAIVA/B), used a master backbone, which includes deletion of the viral virulence element, the NS1 (non-structural protein 1) (DeLNS1), engineered to express one or more antigens of the Sars-CoV-2 (herein, CoV2Ag). The chimeric virus strain is referred to generally herein, as DelNS1-A/B-Sars-CoV-2-CoV2Ag. The DelNS1-A/B-Sars-CoV-2-CoV2Ag strain preferably shows spontaneous cold adaption with preference to grow at 30-33° C. Compositions including the chimeric virus also provided as a co-composition with a LAIVA/B. The DelNS1-A/B-Sars-CoV-2-CoV2Ag strain can be used to protect a subject in need thereof, against a challenge of Sars-CoV-2. The co-compositions can be used to protect a subject in need thereof, against a challenge of Sars-CoV-2 and influenza A and/or B.