The biggest US study yet to examine the superiority of N-95 masks over cheaper, looser-fitting masks has found they do not afford any better protection against respiratory infections.

The study, led by the Centers for Disease Control and Prevention, found no significant difference in the incidence of laboratory-confirmed influenza among healthcare workers randomised to wear either N-95 or surgical masks.

The study was conducted over peak flu seasons of 2011-15 and involved almost 3000 healthcare workers at 137 sites, including primary care facilities, dental clinics and EDs.

Participants wore the devices during the 12-week block when viral respiratory infections were predicted to be highest for each year.