For a long time, influenza has been believed to be droplet borne, not airborne. That is, it would take a droplet of gunk to carry an infectious level of virus. This means you would be in danger from being sneezed on, but not from breathing the air after the sneeze.
A small study in 2011 began to cast doubt on this theory. These researchers found that some, but not all, people suffering from influenza were able to aerosolize the virus, expelling a fine enough mist of gunk that it would indeed remain airborne in an up to 6 foot radius around them. I do not know if this study has been repeated or debunked, but it did leave a lasting impression within the health care field.
The CDC still recommends “droplet precaution” for influenza, meaning gloves, eye protection and gowns when doing things involving bodily fluids, and masks when within 3 feet of the patient. They have not (yet?) upgraded influenza to airborne precautions, which would mean isolation rooms with special air treatment.
[QUOTE=http://www.cdc.gov/flu/professionals/infectioncontrol/healthcaresettings.htm]
Influenza Modes of Transmission
Traditionally, influenza viruses have been thought to spread from person to person primarily through large-particle respiratory droplet transmission (e.g., when an infected person coughs or sneezes near a susceptible person). Transmission via large-particle droplets requires close contact between source and recipient persons, because droplets generally travel only short distances (approximately 6 feet or less) through the air. Indirect contact transmission via hand transfer of influenza virus from virus-contaminated surfaces or objects to mucosal surfaces of the face (e.g., nose, mouth) may also occur. Airborne transmission via small particle aerosols in the vicinity of the infectious individual may also occur; however, the relative contribution of the different modes of influenza transmission is unclear. Airborne transmission over longer distances, such as from one patient room to another has not been documented and is thought not to occur. All respiratory secretions and bodily fluids, including diarrheal stools, of patients with influenza are considered to be potentially infectious; however, the risk may vary by strain. Detection of influenza virus in blood or stool in influenza infected patients is very uncommon.
[/QUOTE]
In an office setting, I’d be okay with my officemate wearing a mask, IF my desk was 6 feet or more away and we could realistically maintain that separation and ASSUMING I’d gotten my flu vaccination (which I have, of course.) Given those conditions, a mask is really an overabundance of caution, but one that would make me feel better, personally.