This is an N95 respirator.

According to the very comprehensive web site pandemicflu.gov, masks like this one—which can be found at hardware stores, although I've heard reports that many stores are sold out—"may help prevent some exposures" to influenza but should be used in conjunction with social distancing (more on that here) and frequent handwashing and/or use of alcohol-based sanitizer (60 percent alcohol or more). Facemasks—defined as "loose-fitting, disposable masks that cover the nose and mouth"—are less effective than respirators, which filter out small particles, which may contain viruses, from the air you breathe.

The US Department of Health and Human Services recommends the following:

Whenever possible, rather than relying on the use of masks or respirators, close contact and crowded conditions should be avoided during an influenza pandemic.

Facemasks should be considered for use by individuals who enter crowded settings, both to protect their nose and mouth from other people's coughs and to reduce the wearers' likelihood of coughing on others; the time spent in crowded settings should be as short as possible.

Respirators should be considered for use by individuals for whom close contact with an infectious person is unavoidable. This can include selected individuals who must care for a sick person (e.g., family member with a respiratory infection) at home.