A trial of the Novavax Covid-19 shows it offers 89% protection against the disease.
According to a preliminary analysis, the jab was nearly as effective in protecting against the more highly contagious variant first discovered in Kent in the south of England.
It has also shown around 60% effectiveness against the South African strain of coronavirus, which has been worrying scientists due to concerns vaccines may not work against it.
The UK has ordered 60 million doses of the Novavax vaccine, which will be manufactured in Stockton-on-Tees. It still requires approval from the Medicines and Healthcare products Regulatory Agency.
Novavax said the trial, which enrolled 15,000 people aged 18 to 84, is expected to be used to apply for regulatory review in Britain, the European Union and other countries. Some 27% of people in the trial are over 65.
The study took place as the more easily transmissible UK variant was circulating, the US company announced in a news release. It did not provide the study data.
Boris Johnson said it is “good news” that the experimental coronavirus vaccine appears to offer strong protection in the UK and South Africa studies.
The prime minister tweeted: “Good news that the @Novavax vaccine has proved effective in UK trials. Thank you to all the volunteers who made these results possible.
“Our medicines regulator will now assess the vaccine, which will be made in Teesside. If approved, we have 60m doses on order.”
Clive Dix, chairman of the UK Vaccine Taskforce, said: “These are spectacular results, and we are very pleased to have helped Novavax with the development of this vaccine. The efficacy shown against the emerging variants is also extremely encouraging.
“This is an incredible achievement that will ensure we can protect individuals in the UK and the rest of the world from this virus.”
The study assessed how effective the vaccine was when transmission of Covid-19 was high in the UK, and with the variant strain first identified in Kent circulating widely.
The UK arm analysis, based on the first 62 cases of Covid-19 identified in the trial, reported 56 cases in people given a placebo (dummy) vaccine while six cases were in those given the Novavax jab.
This part of the trial showed the jab was 89% effective against Covid-19.
More than half of cases related to the UK strain of the virus, with the vaccine offering 86% protection against this particular strain.
Against the original strain that has circulated since the start of the pandemic, the vaccine was 96% effective.
Overall, data from more than 20,000 people, including a trial in South Africa, has now been reported in full.
In the South African arm of the trial, where most cases of Covid-19 were the South African strain, the jab was 60% effective in preventing mild, moderate and severe coronavirus among those without HIV.
Including the HIV positive participants, whose immune systems are compromised, overall the protection was just over 49%.