U.S. pharmaceutical giant Pfizer Inc. said Monday that its experimental vaccine was more than 90 percent effective in preventing COVID-19 during a late-stage clinical study, raising expectations of a breakthrough in the global fight against the coronavirus pandemic.

Pfizer is expected to apply for emergency use authorization in the United States for the potential vaccine as early as this month, after collecting further safety data. The company has an agreement with the Japanese government to supply the Asian country with 120 million vaccine doses, enough for 60 million people or roughly half its population.

A pedestrian wearing a protective mask walks past Pfizer Inc. headquarters on July 22, 2020 in New York City.(Getty/Kyodo)

Pfizer and German partner BioNTech SE are the first among U.S. and European drugmakers to prove their vaccine effective against the disease caused by the novel coronavirus in final-stage clinical trials.

The interim analysis from phase-three study, which began in late July and has enrolled more than 43,000 participants to date, evaluated 94 confirmed cases of COVID-19 in trial participants.

The case split between vaccinated individuals and those who received dummy shots indicates a vaccine efficacy rate above 90 percent, Pfizer said in a press release, adding that protection was achieved 28 days after the initiation of the vaccination, which consists of a two-dose schedule.

No serious safety concerns have been observed. As the study continues, the final vaccine efficacy percentage may vary, according to Pfizer.

The clinical trial will continue through to final analysis at 164 confirmed cases in order to collect further data.

The results demonstrate that the vaccine can "help prevent COVID-19 in the majority of people who receive it," Pfizer said.

U.S. President Donald Trump, who repeatedly said the country was "rounding the corner" of the pandemic during his re-election campaign, tweeted Monday, "VACCINE COMING SOON. REPORT 90% EFFECTIVE. SUCH GREAT NEWS!"

Democrat Joe Biden, who has declared victory in the U.S. presidential election that took place last Tuesday, also welcomed the news, but more cautiously.

"It is also important to understand that the end of the battle against COVID-19 is still months away," he said in a statement.

"This news follows a previously announced timeline by industry officials that forecast vaccine approval by late November. Even if that is achieved, and some Americans are vaccinated later this year, it will be many more months before there is widespread vaccination in this country," he said.

He also called on the public to make progress toward improving mask-wearing and social-distancing habits so as to prevent the situation from deteriorating further.

The total number of confirmed coronavirus cases in the United States since the pandemic began exceeded 10 million on Monday, making it the first country to hit the grim milestone, according to Johns Hopkins University data.

More than 237,000 people have died due to COVID-19 in the United States, a higher death toll than in any other country in the world.

Globally, about 51 million cases have been confirmed with about 1.3 million deaths since the pandemic started.