The Democratic nominee also accused his election rival Trump of politicizing the vaccine development process and said he does not trust the public statements by the president, who said Tuesday night that a vaccine was just weeks away from completion.
Whether the Trump administration can hurry a safe vaccine into wide production has become a focal point of the 2020 election campaign, in which polls show Biden leading Trump.
"The president's first responsibility is to protect the American people, and he won't. And it's utterly disqualifying," Biden told reporters, citing Trump's "lack of seriousness" in handling the pandemic.
Speaking after receiving a briefing by public health experts, Biden discussed how a Covid-19 vaccine would help American life return to normal, but said the process should be guided by science and safety, not politics.
"So let me be clear: I trust vaccines, I trust scientists, but I don't trust Donald Trump," Biden said. "At this moment the American people can't either."
Biden has stressed he supports a rapid rollout of a vaccine, but only if it is shown to be safe and effective, if there is full transparency regarding the science of the work, and if it is distributed "equitably."
With Trump insisting that a vaccine was now just "weeks" away, a leading health expert in his own administration warned Wednesday that a vaccine for broad public use would not be available until mid-2021 at the earliest.
Experts say a coronavirus vaccine is among the best ways to halt the march of a pandemic that has killed more than 196,000 Americans.
On Tuesday Trump accelerated his own already optimistic predictions, saying a vaccine may be available even before the November 3 presidential election.
"We're within weeks of getting it, you know -- could be three weeks, four weeks," he told a town hall question-and-answer session with voters in Pennsylvania aired on ABC.
Only hours earlier, speaking to Fox News, Trump had said a vaccine could come in "four weeks, it could be eight weeks."
But Centers for Disease Control and Prevention director Robert Redfield testified before Congress Wednesday that any vaccine this year would not be for widespread use.
"I think there will be (a) vaccine that initially will be available sometime between November and December, but very limited supply and will have to be prioritized," he told a Senate panel.
"If you're asking me when is it going to be generally available to the American public so we can begin to take advantage of (a) vaccine to get back to our regular life, I think we're probably looking at late second quarter, third quarter 2021."
Democrats have expressed concern that Trump is pressuring government health regulators and scientists to approve a rushed vaccine in time to help his uphill bid for reelection.
Trump also raised eyebrows when asked at the town hall why he had downplayed the gravity of the pandemic in its early months.
"I didn't downplay it," Trump replied. "I actually, in many ways, I up-played it in terms of action."
But Trump himself told journalist Bob Woodward during taped interviews that he had deliberately decided to "play it down" to avoid alarming Americans.
- 'Science knows' -
The president, who is rarely seen wearing a mask in public and long refused to push Americans to adopt the habit, told the town hall that "a lot of people don't want to wear masks and people don't think masks are good."
The comment caught wide flak, including from Biden, who also knocked Trump for saying the Democrat declined to institute a mask mandate.
"I'm not the president, he's the president," Biden said.
Trump's anti-mask message got a dressing down of sorts by Redfield too, as the CDC director held up a medical mask to senators and said "I might go so far as to say that this facemask is more guaranteed to protect me against Covid than when I take a Covid vaccine."
Biden, 77, has slowly ramped up campaign appearances, including a trip Tuesday to Florida where he courted Hispanic voters.
But he has yet to match the campaign trail fervor of the 74-year-old Republican incumbent, who has hosted numerous rallies in swing states, often with attendees not wearing masks or observing social distancing guidelines.
