Shares of the New York-based company were off slightly to $37.10.
If the results are positive, CEO Albert Bourla said, Pfizer will immediately file for emergency use authorization in the U.S.
Bourla made his comments during a Q&A with the International Federation of Pharmaceutical Manufacturers & Associations.
He said Pfizer already has enrolled 23,000 volunteers in the phase 3 trial that began in late July and hopes to sign up at least 30,000 participants, between the ages of 18 and 85.
The test is expected to take place across 120 sites worldwide, including 39 U.S. states.
The companies said the vaccine "was well tolerated with mild to moderate fever in fewer than 20% of the participants."
In July, Pfizer agreed to provide 600 million doses of its developing coronavirus vaccine to the U.S. government. Pfizer and BioNTech will receive $1.95 billion for the first 100 million doses of their BNT162b2 vaccine, once it is approved by regulators, with the potential for a further 500 million doses to be manufactured thereafter.
More than 160 coronavirus vaccines are under development worldwide, according to the World Health Organization.
The Centers for Disease Control has urged governors to be prepared for the distribution of a coronavirus by Nov. 1, prompting concerns of political interference among some health officials going into the presidential election.