Just four in 10 Americans say attending a Fourth of July celebration this year feels risky — about half as many as a year ago, according to the latest installment of the Axios/Ipsos Coronavirus Index.

The big picture: Our weekly national survey finds broad awareness and concern around the emerging Delta variant. But people's behaviors really aren't changing in the face of that threat.

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.

• "The vaccine and, then, governments at every level saying it’s ok to go out: it’s those in combination."

Between the lines: A noteworthy minority of respondents — 14% — say they believe they got the virus at some point since the start of the pandemic but that they never got tested, or never tested positive.

• Statistically, those in that group are far more likely than other Americans not to have gotten the vaccine yet and to say that they won't get it.
• "Some people are essentially thinking, 'Well, I don’t have to have it because I already have immunity,'" said Ipsos pollster and senior vice president Chris Jackson. "But we don’t know if they had it, and we don’t know if they have immunity."

By the numbers: 41% of U.S. adults say attending an Independence Day celebration this year carries either a moderate or high risk, down from 78% when we asked the same question a year ago.

• A year ago, a full 45% of Americans said it was a large risk, with 33% calling it a moderate risk, 17% a small risk and 6% no risk.
• Now, 14% see it as a large risk, 27% as a moderate risk, 36% a small risk and 23% no risk.

What we're watching: 84% of respondents said they're aware of the Delta variant of the virus, and of those, 72% say they're concerned about it.

• But if there were a spike in coronavirus cases in their state, just four in 10 say they'd self quarantine, less than six in 10 would stop visiting friends and family and half would curb their non-grocery shopping trips — all significant drops in behavior modification compared to a year ago.
• More said they would curb socializing outside the home if their governor or the Centers for Disease Control and Prevention advised them to do so.

Methodology: This Axios/Ipsos Poll was conducted June 25-28 by Ipsos' KnowledgePanel®. This poll is based on a nationally representative probability sample of 1,016 general population adults age 18 or older.

• The margin of sampling error is ±3.2 percentage points at the 95% confidence level, for results based on the entire sample of adults.