Interim Guidance for the Use of Masks to Control Seasonal Influenza Virus Transmission – CDC

Persons who are diagnosed with influenza…should remain at home until the fever is resolved for 24 hours…and the cough is resolving to avoid exposing other members of the public. If such symptomatic persons cannot stay home during the acute phase of their illness, consideration should be given to having them wear a mask in public places when they may have close contact with other persons. 

No recommendation can be made at this time for mask use in the community by asymptomatic persons, including those at high risk for complications, to prevent exposure to influenza viruses.