The Pfizer-BioNTech Covid vaccine has been authorised for emergency use in the US.
The US Food and Drug Administration (FDA) said the authorisation was a "significant milestone" in the pandemic.
Offering up to 95% protection against coronavirus, the vaccine was deemed safe and effective by the FDA.
Shots for health workers and nursing home residents are expected to begin in the coming days.
President Donald Trump said late on Friday that Pfizer had “passed the gold standard of safety” in a video statement hailing the vaccine as “one of the greatest scientific accomplishments in history”.
READ MORE: Regulators issue warning after allergic reactions from coronavirus vaccine
"Today our nation has achieved a medical miracle," Mr Trump said. "We have delivered a safe and effective vaccine in just nine months."
In the first shipments, some three million doses of the vaccine are expected.
A similar amount is said to be held in reserve for the second doses.
The Pfizer vaccine has already been rolled out in the UK, with the first doses being administered earlier this week.
FDA head Stephen Hahn was apparently told to approve the vaccine for emergency use by Friday or leave his job, according to US media - however, he called this claim "untrue".
Reacting to the authorisation, he said on Twitter: "The FDA’s authorization for emergency use of the first #COVID19 vaccine is a significant milestone in battling this devastating pandemic that has affected so many families in the United States and around the world.
"Today’s action follows an open & transparent review process that included input from independent scientific & public health experts and a thorough evaluation by the agency’s career scientists.
"This thorough review is to ensure this vaccine met FDA’s rigorous, scientific standards for safety, effectiveness, and manufacturing quality needed to support emergency use authorization.
"The tireless work to develop a new vaccine to prevent this novel, serious, and life-threatening disease in an expedited timeframe after its emergence is a true testament to scientific innovation and public-private collaboration worldwide."
Why are you making commenting on The Herald only available to subscribers?
It should have been a safe space for informed debate, somewhere for readers to discuss issues around the biggest stories of the day, but all too often the below the line comments on most websites have become bogged down by off-topic discussions and abuse.
heraldscotland.com is tackling this problem by allowing only subscribers to comment.
We are doing this to improve the experience for our loyal readers and we believe it will reduce the ability of trolls and troublemakers, who occasionally find their way onto our site, to abuse our journalists and readers. We also hope it will help the comments section fulfil its promise as a part of Scotland's conversation with itself.
We are lucky at The Herald. We are read by an informed, educated readership who can add their knowledge and insights to our stories.
That is invaluable.
We are making the subscriber-only change to support our valued readers, who tell us they don't want the site cluttered up with irrelevant comments, untruths and abuse.
In the past, the journalist’s job was to collect and distribute information to the audience. Technology means that readers can shape a discussion. We look forward to hearing from you on heraldscotland.com
Comments & Moderation
Readers’ comments: You are personally liable for the content of any comments you upload to this website, so please act responsibly. We do not pre-moderate or monitor readers’ comments appearing on our websites, but we do post-moderate in response to complaints we receive or otherwise when a potential problem comes to our attention. You can make a complaint by using the ‘report this post’ link . We may then apply our discretion under the user terms to amend or delete comments.
Post moderation is undertaken full-time 9am-6pm on weekdays, and on a part-time basis outwith those hours.
Read the rules here