Michael R. Caputo, a spokesman for Mr. Azar, said October was not the goal.
“Everybody at H.H.S. hopes Operation Warp Speed will achieve 300 million doses of a safe and effective Covid vaccine for Americans by January 2021,” he said. “We know that’s optimistic. I have never heard mention of any other timeline, and certainly not from the secretary.”
“Careless talk about career F.D.A. regulators somehow approving an unsafe and ineffective vaccine just for politics only undermines confidence in the public health system,” he added.
It is not clear that a vaccine approval shortly before the election would be an “October surprise” sufficient to alter the outcome of the vote. An announcement could give Americans hope that the end is in sight. But some Republican strategists said that it might not help Mr. Trump because his opponent, former Vice President Joseph R. Biden Jr., the presumptive Democratic nominee, would surely continue the vaccine process if elected.
“Does it turn everything around for him politically? I don’t know,” said Sarah Longwell, a conservative strategist and prominent Republican opponent of Mr. Trump who regularly conducts focus groups and has found that public attention is more focused on government relief checks and school reopenings.
“If the vaccine is an October surprise, there’s a lot of other things that are cutting against” it as a game-changer, she said.
The drug companies find themselves caught in the middle. While eager to bring products to market as quickly as possible, they face risks in moving too quickly in order to fit an election calendar, analysts said.
“They are acutely aware of the political dynamic here,” said Rob Smith, the director of Capital Alpha Partners, a research firm. A vaccine that flopped would jeopardize their broader business, he said, and it would not make sense “to take a huge reputational risk not just for your vaccine but for all the products across your portfolio to benefit the president politically.”