The director of the Centers for Disease Control and Prevention predicted Wednesday that most of the American public will not have access to a vaccine against the novel coronavirus until late spring or summer of next year.

At a Senate hearing on the government's response to the pandemic, CDC director Robert Redfield adhered to President Donald Trump's oft-stated desire for a safe and effective vaccine to become available in November or December - perhaps just before the presidential election seven weeks away.

But Redfield said the vaccine will be provided first to people most vulnerable to covid-19, the disease caused by the virus, and supplies will increase over time, so Americans who are lower priority for the protection will be offered the shot more gradually. For it to be "fully available to the American public, so we begin to take advantage of vaccine to get back to our regular life," he said, "I think we are probably looking at late second quarter, third quarter 2021."

Though any individual vaccinated should benefit, he said, the progressive widening of its availability means there will be a time lag between when a vaccine is approved and when it could have a measurable effect in controlling the pandemic. That might be six to nine months after the day it is approved by federal drug regulators, Redfield predicted.

The comments were the most detailed time frame outlined so far by the leader of the government's main public health agency.

They came as Trump has latched onto the prospect of a vaccine as crucial to his prospects for a second term, with low approval ratings among voters for his handling of the worst public health crisis that the country and world have confronted in a century. A vaccine also is widely regarded as a pivot point for Americans to be unfettered from the constraints the pandemic has imposed on daily life - from recreation such as concerts and movie theaters to workplaces that remain shuttered.

A race is underway internationally among pharmaceutical makers to develop vaccines that are safe and effective against the virus, which has infected nearly 6.6 million people in the United States and killed almost 200,000. Developing a vaccine typically takes years, but researchers are working with unprecedented speed. U.S. researchers in January established the goal of a world-record pace of developing an inoculation against the coronavirus within a year to 18 months.

Now, seven experimental vaccines are in the final stage of testing - giving it to thousands of people to check its effectiveness and whether it is safe - before submitting it for federal approval. A debate is raging over whether the Food and Drug Administration should hasten a vaccine's availability by employing emergency authority it has before going through the process of a formal approval.

The CDC told states this month they should be ready to receive a coronavirus vaccine as early as Nov. 1 - two days before the election - prompting allegations from critics that the date was politically motivated.

Redfield pressed back again such suggestions from committee Democrats during an appearance Wednesday before a Senate subcommittee with jurisdiction over the Department of Health and Human Services, of which the CDC is a part. He said the advice to states was based on the pace of the science, not any electoral considerations. And he said his agency was eager to avoid a repetition of a problem that emerged during a pandemic of the H1N1 virus in 2009, when a vaccine became available and states were not ready to receive and distribute it.

"We don't want to repeat that hiccup," Redfield told senators.

He also said the government does not have an estimated $6 billion it needs for the distribution of a coronavirus vaccine. Such funds were proposed in pandemic relief legislation that Congress has not adopted, among partisan disputes over how much more aide the government should provide for laid-off workers and a variety of other purposes.

Providing that money, Redfield said, "is as urgent as getting the manufacturing facilities up."