The vaccine developed by Oxford University was 90% effective in preventing Covid-19 when it was administered as a half dose followed by a full dose at least one month apart, according to data from the late-stage trials in Britain and Brazil.
No serious safety events related to the vaccine have been confirmed and it was well tolerated across both dosing regimens, it said.
"This vaccine's efficacy and safety confirm that it will be highly effective against Covid-19 and will have an immediate impact on this public health emergency," Pascal Soriot, Astra's chief executive, said in a statement.
AstraZeneca will have 200 million doses by the end of 2020, with 700 million doses ready globally by the end of the first quarter of 2021, operations executive Pam Cheng said on Monday.
The vaccine's effectiveness depended on the dosing, and fell to just 62% when given as two full doses rather than a half-dose first. But scientists cautioned against seeing this as evidence that it would be less useful than rival vaccines from Pfizer and Moderna, which each prevented about 95% of cases according to interim data from their late-stage trials.
"I think it is a real fool's errand to start trying to pick these three (Pfizer/Moderna/Astra) apart on the basis of snippets of phase 3 data from press releases," said Danny Altmann, professor of immunology at Imperial College London.
"For the bigger picture, my suspicion is that by the time we are a year down the line, we'll be using all three vaccines with about 90% protection - and we'll be a lot happier."
Scientists also noted there may be advantages to AstraZeneca's vaccine.
"Importantly, from what we have heard the vaccine seems to prevent infection not just disease. This is important as the vaccine could reduce the spread of the virus as well as protect the vulnerable from severe disease," said Peter Horby, a professor of emerging infectious diseases and global health at the University of Oxford,
AstraZeneca's vaccine can also be distributed more easily because it can be kept at refrigerator temperature, unlike the drugs from Pfizer and Moderna which have to be stored frozen. That would make the AstraZeneca shot easier to transport and store globally, particularly in lower and middle-income countries.
The British drugmaker's preliminary trial results mark a fresh breakthrough in the fight against a pandemic that has killed nearly 1.4 million people and roiled the global economy.
Britain is among countries that pre-bought large quantities of the new vaccine. Officials said its success means normal life can return sooner. It was "incredibly exciting news the Oxford vaccine has proved so effective in trials," said Prime Minister Boris Johnson.
There would be 20 million doses in Britain by the end of the year, with 70 million doses for the UK by the end of Q1 2021.
Shares and oil prices rose as investors bet the rollout of another vaccine would revive the global economy next year even as virus case numbers surge.
The STOXX index of Europe's 600 largest shares rose 0.5% to its highest since February but AstraZeneca shares fell more than 2% as traders perceived the efficacy data as disappointing compared with rivals.
The interim analysis was based on 131 infections among participants who received the vaccine and those in a control group who were given an established meningitis shot.
Public health experts say the world will need many vaccines to meet global demand.
The AstraZeneca vaccine uses a modified version of a chimpanzee common cold virus to deliver instructions to cells to fight the target virus, a different approach from the new technology known as messenger RNA (mRNA) deployed by Pfizer/BioNTech and Moderna.
AstraZeneca, one of Britain's most valuable listed companies, will now immediately prepare regulatory submission of the data to authorities around the world that have a framework in place for conditional or early approval.
It will also seek an emergency use listing from the World Health Organization to speed up availability in low-income countries. In parallel, the full analysis of the interim results is being submitted for publication in a peer-reviewed journal. - Reuters
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