You're misinterpreting
the survey.
The question was how worried are you that the Trump administration would pressure the FDA to rush the vaccine and cut corners. 85% of Democrats were worried, compared to 61% of independents and 35% of Republicans.
The 54% was for if they would get the vaccine before the election (survey was from Labor Day) if it was approved by the FDA and free. Keep in mind that 81% of Americans felt that the vaccine wouldn't be ready by then. In other words, the first answer is based on the feeling that a vaccine in November would be rushing, rightly or wrongly; the general public isn't very smart.
The standard messaging from most Democrats at that point was they'd take it if the FDA approved it. Like I said, sure some definite partisanship, but nothing remotely like the anti-vax messaging you've seen from Republicans.
“Let me be clear: I trust vaccines,” Mr. Biden said. “I trust scientists. But I don’t trust Donald Trump, and at this moment, the American people can’t either... “Scientific breakthroughs don’t care about calendars any more than the virus does,” he said. “They certainly don’t adhere to election cycles. And their timing and their approval and their distribution should never, ever be distorted by political considerations. It should be determined by science and safety alone.”