By Bojan Pancevski and Jared S. Hopkins

Pfizer Inc. laid out a timetable for reaching key milestones in the development of its Covid-19 vaccine that could mean the shots start becoming available in the U.S. before year's end.

Chief Executive Albert Bourla said Friday the company could start to see from a large study whether the vaccine works by the end of this month and would have data on its safety by the third week of November. If the preliminary results indicate the vaccine can work safely, Pfizer could ask U.S. health regulators to permit use by late November, Mr. Bourla said.

The timetable, which Mr. Bourla provided in a letter posted to Pfizer's website, suggests the shots could start going into use in late November, or more likely in December, since regulators would probably need some time to review the study data as well as Pfizer's manufacturing operations.

New York-based Pfizer is developing its vaccine candidate with German partner BioNTech SE.

It is far from certain the vaccine would prove to work safely in the trial now enrolling some 44,000 volunteers. And the timetable could be pushed back for a number of reasons, including if it takes longer than Pfizer expects for study subjects to get exposed to the virus.

Also, Pfizer wouldn't seek its vaccine's authorization for use if it doesn't prove to work safely.

Drugmakers don't typically detail research, development and regulatory timelines in such detail. Mr. Bourla, who has been using letters to employees and now the public to address concerns the shots will be rushed too quickly into use, said Pfizer is doing so to clear up confusion.

President Trump said in the Sept. 29 presidential debate that he had spoken with vaccine makers including Pfizer and a shot was weeks away. Mr. Trump had said previously a vaccine could be available before Election Day. Pfizer's timeline puts a pre-election clearance for its candidate out of reach.

"To ensure public trust and clear up a great deal of confusion, I believe it is essential for the public to understand our estimated timelines," Mr. Bourla said. Earlier this month, he pledged in a letter to employees that politics wouldn't affect the vaccine's development.

The vaccine candidate from Pfizer and BioNTech is among the most advanced in development, along with candidates from AstraZeneca PLC, Moderna Inc. and Johnson & Johnson. Yet trials for AstraZeneca and J&J's vaccines are on hold, at least in the U.S., as safety issues are probed.

The studies' pauses, combined with the timeline laid out by Pfizer, suggest the company's shot could be one of the first, if not the first, to be sent to the U.S. Food and Drug Administration for review. Mr. Bourla didn't disclose timing for similar applications anywhere else in the world.

Given the urgent need for a vaccine, the FDA plans to conduct a speedier review than normal, which would result in what it calls an authorization for emergency use. The FDA, however, has established standards any Covid-19 vaccine would have to meet similar to those required for a regular approval of the shots.

After filing for authorization, the FDA is expected to take some time to consider the application. One of the first steps will involve review by an outside committee of vaccine experts, which FDA officials have said will accompany any Covid-19 vaccine seeking a green light.

For months, Pfizer has been updating the FDA on its program and progress, a sort of real-time information feed that isn't normal in regulatory review. The goal is for the agency to be familiar with the program so it can assess trial results more quickly.

Mr. Bourla has long given a late October timeline for seeing data whether its vaccine is effective. He was referring to results from a preliminary look at the late-stage study's progress. Under Pfizer's plans for the study, researchers can take a look at data after 32 subjects developed symptomatic Covid-19 to see whether the people got the vaccine or a placebo.

The peek would give a sense of whether the vaccine was protecting people against the virus.

Such early looks require a higher bar of efficacy than a final look because it is based on a relatively small number of cases. Pfizer could seek the vaccine's authorization if the shot proved in that early look to meet the ambitious goals for effectiveness, and if it then appeared to be safe in subjects who had gone two months after getting vaccinated without serious side effects.

By that time, the company will provide the FDA materials showing it could properly manufacture the vaccine, Mr. Bourla said in his letter.

Unlike some of the other drugmakers working on vaccines, Pfizer has said it plans to make a profit from its shot. The company hasn't received any government support for its manufacturing or research, while some rivals have. In the recent letter to employees, Mr. Bourla said that at Pfizer "every ounce of our ability has been spent and nearly $2 billion put at risk."

In July, Pfizer and BioNTech reached a $1.95 billion deal with the U.S. to supply 100 million doses. The U.S. pact suggests a $19.50 price a dose, or $39 for the two-dose shot, which is in line with what the private sector pays for flu vaccines.

The vaccine could fetch nearly $13 billion in global sales next year, which would be split between Pfizer and BioNTech, according to Morgan Stanley analysts.

As the West largely waits out the data from these human trials, China and Russia have rolled out their own vaccines and authorized their limited use for some parts of their populations and beyond.

While the timeline laid out by Pfizer on Friday is limited to its application for U.S. emergency-use authorization, Europe's top regulator could act quickly on similar data submissions from Pfizer and BioNTech. BioNTech said Friday a European application for emergency use would quickly follow one made to the FDA.

Such data would be immediately reviewed by the European Medicines Agency, a senior EMA official said. The EMA, which regulates drugs across the European Union, could then issue what it calls a conditional marketing authorization, similar to emergency-use authorization in the U.S.

Pfizer and BioNTech have been racing to increase production of its vaccine candidate to meet the world's needs, assuming the shot wins a regulatory green light. The two have committed to supplying over 450 million doses this year and next year, if the vaccine proves to work safely.

The EU ordered 200 million doses with an option for another 100 million. The government of Japan ordered 120 million doses and Britain ordered 30 million.

BioNTech and Pfizer previously set a target to produce up to 100 million vaccines globally by the end of this year. That initial batch would only be enough for 50 million people, though, because the vaccine, known as BNT162, consists of two shots. The two companies haven't disclosed how many doses they have already made.

--Drew Hinshaw contributed to this article.

Write to Bojan Pancevski at bojan.pancevski@wsj.com and Jared S. Hopkins at jared.hopkins@wsj.com

(END) Dow Jones Newswires

10-16-20 1158ET