LOS ANGELES - COVID-19 "fatigue" is having a negative effect on some protective measures that people are taking to guard against the coronavirus -- although mask-wearing is up, according to a new USC survey.Protective measures such as avoiding close contact with non-household members and staying home are waning as the pandemic drags on, the study reported.The findings were called worrisome, given the importance of the "Swiss cheese" model of pandemic defense -- in which multiple layers of protection block the spread of the new coronavirus.Researchers said that protective behaviors remain important until a large percentage of the population is vaccinated."There has been a lot of talk about 'pandemic fatigue,' and this study clearly shows.