The results add to other early findings from studies of vaccine roll-outs in Israel, Scotland and England, which have also pointed to high effectiveness from the first doses.
The study and its results have yet to be independently peer-reviewed by other scientists, but could bring the world closer to understanding how vaccines impact transmission.
They are also in talks to test a vaccine modified to protect specifically against the highly transmissible new variant first found in South Africa.
By the fourth week after the initial dose, the Pfizer and AstraZeneca COVID-19 vaccines cut the risk of hospitalisation by up to 85 per cent and 94 per cent, the study showed.
Pfizer's vaccine is currently authorized to be taken 21 days apart.
The companies said the 200 million doses are expected to be delivered this year, with an estimated 75 million of them in the second quarter.
One vial of the Pfizer/BioNTech vaccine is now meant for six shots, but it takes special syringes that retain a low volume of solution after an injection.
In theory, lipids should be easy to produce on a large scale, but it gets complicated when the goal is to produce billions of new COVID-19 vaccines for the world.
Medical professionals in the United States were first to discover in December that they could get six doses from each vial by using special syringes.
“It’s not like adding more water to the soup,” said vaccine specialist Maria Elena Bottazzi of Baylor College of Medicine.
The latest disagreement came after AstraZeneca rejected the EU's accusation that the company had failed to honour its commitments to deliver coronavirus vaccines.
While it's far from unusual that new drugs come with side effects and potential safety concerns, the deaths of elderly people in Norway have stirred worry.
With the first vaccine rollouts and a surge in coronavirus infections, experts are debating what to do about half of the people in clinical trials that got a dummy shot.
Its addition allows countries to expedite their own regulatory approval process for the vaccine.
The first person in Germany to be immunized with the Pfizer-BioNTech vaccine was 101-year-old Edith Kwoizalla.
Only a third of the first shipment of Pfizer vaccine doses have been given across the U.S., putting the government's target for 20 million vaccinations this month in doubt.
Netanyahu said he wanted to be the country's first recipient to set a personal example and to encourage Israelis to get the shot.
A U.S. Food and Drug Administration official said at a press conference that the allergic reactions had been reported in more than one state, including in Alaska.
“The American people can be confident: we have one and perhaps within hours two safe vaccines,” Pence said, referring to expected FDA approval for Moderna’s vaccine.
Trump will get the vaccine himself as soon as his medical team determines it is best, White House Press Secretary Kayleigh McEnany said on Tuesday.