(CNN) Just because states have been asked to have a vaccine distribution plan doesn't mean the public should expect to get shots this fall, doctors say.
The Centers for Disease Control and Prevention told state and local public health officials to prepare to distribute a possible Covid-19 vaccine as soon as late October.
Many health experts say a safe and effective vaccine might not be publicly available until early 2021. But it's possible the Food and Drug Administration could give an emergency use authorization for a vaccine to be distributed before its Phase 3 clinical trial is over, if the data is very promising.
Some doctors say they'd rather see a vaccine go through all the rigors to get a full FDA approval.
"How can you justify a substandard or lesser review for something that would be injected in tens of millions, maybe hundreds of millions of Americans?" said Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine.
Three Covid-19 vaccines in the US are now in Phase 3 trials, and officials have insisted no vaccine will be distributed to the public until it's deemed effective and safe.
And that's not likely to happen by late October, said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.
"If you look at the projection, of the enrollment (of trial participants) and the kinds of things you'll need to get a decision about whether the vaccine is safe and effective, most of us project that that's going to be by November, December, by the end of the year," Fauci told CNN on Thursday.
"Could this be earlier? Sure ... that's unlikely (but) not impossible."
President Donald Trump has touted the idea that a vaccine could be out to the public by the November 3 election. But vaccine experts have said that's not realistic.
Any decision about approving or authorizing a coronavirus vaccine will be driven by science and evidence, Health and Human Services Secretary Alex Azar said.
"Thanks to President Trump's leadership of this Operation Warp Speed, we're making historic progress towards a vaccine," Azar said on CBS Thursday.
He said that he doesn't know when the data will come, as it will depend on the rate of infection in the communities where the vaccine candidate and placebo have been administered.
"President Trump has made it clear, and I've made it clear, these decisions will be driven by the standards of science and evidence and FDA's gold standards," he said.
With the upcoming holiday weekend, Fauci made a "plea to the American public" not to repeat the mistakes from past holidays.
"We don't want to see a repeat of the surges that we have seen following other holiday weekends," he said.
"That doesn't mean you have to lock yourself in a room and not enjoy what hopefully will be a nice weekend for people. But there are certain fundamental things that you can do and still enjoy yourself."
That includes wearing a mask while socializing, keeping a safe distance from others, avoiding crowds, and keeping gathering outside, not indoors.
Many states suffered spikes in new cases, hospitalizations and deaths after the Memorial Day and July 4 holidays. But what happens over Labor Day weekend is critical.
"It's important for two reasons," Fauci said. "We don't want to see a surge under any circumstances. But particularly as we go on the other side of Labor Day and enter into the fall ... we don't want to go into that with another surge that we have to turn around again."
Health experts say the double whammy of a coronavirus pandemic coinciding with the flu season this fall could strain hospital capacity. About 140,000 to 810,000 Americans are hospitalized with the flu each year, according to CDC estimates.
That's why doctors say getting a flu vaccine this year is especially important.
Kentucky Gov. Andy Beshear also stressed the importance of safety precautions as his state hosts the Kentucky Derby this Labor Day weekend, which will run without fans in the stands.
"Please, let's not look back and say something as special as what this weekend can be turned into the time when this virus got out of control," the governor said.
A CDC forecast that pulls data from 35 modeling groups foresees the death toll from Covid-19 increasing to between 200,000 to 211,000 by September 26.
"This week's national ensemble forecast predicts that weekly reports of new Covid-19 deaths may decrease nationally over the next four weeks, with 3,300 to 7,500 new deaths reported during the week ending September 26, 2020," the CDC said on its website.
The CDC forecast released on August 13 predicted a death toll of nearly 189,000; the range it gave was between 181,375 to 201,431 deaths.
More than 186,000 people have died from Covid-19, according to Johns Hopkins University. The CDC, who total lages behind Johns Hopkins, says more than 185,000 death certificates list Covid-19 as a cause of death.
College campuses in at least 40 states have seen outbreaks of the virus, news that has prompted elected officials to caution students to be more careful.
"I want to urge all of the college students as we go into the Labor Day weekend, I understand many will probably not be going home since they just got on campus. So they'll be around and they'll have some free time," Arkansas Gov. Asa Hutchinson said. "You've got to be cautious over this weekend."
The governor said that 211 of the 969 new cases reported in the state are from Washington County, home to the University of Arkansas.
In the county, four out of every five positive tests were among people between the ages of 18 and 24.
Meanwhile, Ohio State University, which typically has 61,000 students on its main campus, has reported a total of 882 cases since mid-August, and averaged a positivity rate of 4.5% for the past week.
Gov. Mike DeWine said the numbers are a result of universities doing "frankly a very good job in testing." But he also asked college students to be careful.
"While all of us, when we were your age, thought we were invincible, you can pass this on, you can get it and pass it on," DeWine said. "And that really is the danger."
In Missouri, Gov. Mike Parson said that approximately 30% of the new cases in the state are among the 18 to 24 population.
"I know there is a lot of concern right now regarding college students," Parson said. "But I want to assure you that our colleges, and our universities have plans in place, and are taking all steps necessary to keep their students and communities as safe as possible."
More than 27,000 students have had positive coronavirus tests, according to CNN's compilation of available data.
Across the US, more than 6.1 million people have been infected with coronavirus.