The coronavirus vaccine from Pfizer – which is due to arrive in the UK before the end of the year – is 95% effective and has passed its safety checks, according to further data from the firm.
The pharmaceutical giant and its partner BioNTech published interim results last week showing the jab could prevent more than 90% of people developing Covid-19.
That data was based on the first 94 volunteers to develop Covid-19, but further figures released on Wednesday are based on the first 170 cases of the virus in the clinical trial.
The vaccine has been tested on 43,500 people in six countries and no safety concerns have been raised.
The UK has secured 40m doses in total of the vaccine, with 10m due in the country by the end of the year if the jab is approved.
People will need two doses, meaning not enough vaccine has been secured for the entire UK population.
Another jab, from US firm Moderna, was shown this week in early data to be almost 95% effective.
The UK has ordered five million doses of that jab, and also awaits the results of the Oxford University and AstraZeneca vaccine study – which is due to report soon.
Changes to the Human Medicine Regulations announced in October will allow the Medicines and Healthcare products Regulatory Agency (MHRA) to authorise temporary supply of vaccines, if one becomes available before 2021.
This means that if a vaccine is found to meet the safety, quality and effectiveness standards by the MHRA then vaccinations can begin without needing to wait for the European Medicines Agency.
The Scottish Government is due to announce plans soon for a nationwide vaccination programme.
The Pfizer vaccine has been shown to produce both an antibody and T-cell response in the body to fight coronavirus.
Pfizer and BioNTech expect to be able to produce up to 50 million vaccine doses globally in 2020 and up to 1.3 billion in 2021.
On Tuesday, Pfizer chief executive Albert Bourla said the firm is preparing to file for emergency use authorisation from the US Food and Drug Administration.