Why it matters: The vaccine's effectiveness so far and its wide availability seem to be acting as a shield, psychologically as well as scientifically. 55% of respondents now say they're wearing masks all or some of the time when they leave the home — the lowest share since we began asking the question in April of last year. As long as people believe the vaccine will protect them from death or sickness, the less likely they are to say they'll mask up or stay home, even if there were another spike in cases. What they're saying: "America’s moved on," said Cliff Young, president of Ipsos U.S. Public Affairs. "The way Americans perceive the world has changed because of the vaccine.