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 University of Southern California (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 that people are less willing to take precautions to limit the risk of infection and slow the spread of the virus,” said John Romley, lead researcher on the study and  a senior fellow …