Administering a shot at a community vaccination and testing site in San Francisco on Aug. 1, 2021. (MIKE KAI CHEN, New York Times file/The Minnesota Star Tribune)

The delta variant was the main reason that people decided to get vaccinated against COVID-19 this summer and why most say they will get boosters when eligible, according to the latest monthly survey on vaccine attitudes by the Kaiser Family Foundation, released on Tuesday morning. But the survey indicated that nearly three-quarters of unvaccinated Americans view boosters very differently, saying that the need for them shows that the vaccines are not working.

That divide suggests that while it may be relatively easy to persuade vaccinated people to line up for an additional shot, the need for boosters may complicate public health officials' efforts to persuade the remaining unvaccinated people to get their initial one.

Another takeaway from the Kaiser Family Foundation survey: For all the carrots dangled to induce hesitant people to get COVID shots — cash, doughnuts, racetrack privileges — more credit for the recent rise in vaccination goes to the stick. Almost 40% of newly inoculated people said that they had sought the vaccines because of the increase in COVID cases, with more than a third saying that they had become alarmed by overcrowding in local hospitals and rising death rates.

"When a theoretical threat becomes a clear and present danger, people are more likely to act to protect themselves and their loved ones," said Drew Altman, the Kaiser Family Foundation's chief executive.

The nationally representative survey of 1,519 people was conducted Sept. 13-22 — during a time of surging COVID deaths, but before the government authorized boosters for millions of high-risk people who had received the Pfizer-BioNTech shot, including those 65 and over and adults of any age whose job puts them at high risk of infection.

Sweeteners did have some role in getting shots in arms. One-third of respondents said that they had gotten vaccinated to travel or attend events where the shots were required.

Two reasons often cited as important for motivating those hesitant to get a vaccine — employer mandates (about 20%) and full federal approval for the Pfizer-BioNTech vaccine (15%) — carried less sway.

Seventy-two percent of adults in the survey said that they were at least partly vaccinated, up from 67% in late July. The latest numbers from the Centers for Disease Control and Prevention are even higher, reporting 77% of the adult population in the United States with at least one shot. The sharpest change in this month was in vaccination rates for Latinos: a jump of 12 percentage points since late July, to 73%, in the number of Latino adults who had received at least one shot.

With the vaccination racial gap narrowing, the political divide has, by far, become the widest, with 90% of Democrats saying that they have gotten at least one dose, compared with 58% of Republicans.

Perhaps reflecting pandemic fatigue, about 8 in 10 adults said that they believed COVID was now a permanent fixture of the health landscape. Just 14% said that they thought "it will be largely eliminated in the U.S., like polio."

This article originally appeared in The New York Times.