AstraZeneca, Oxford COVID-19 vaccine up to 90% effective in late-stage trials

Efficacy ranged from 62% to 90%, depending on dosage

LONDON— AstraZeneca PLC and the University of Oxford said their Covid-19 vaccine was as much as 90% effective in preventing infections without serious side effects in large clinical trials, boosting hopes that a third Western-developed shot could be authorized for use before the end of the year.

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The partners said Monday that there were no serious safety events related to the vaccine and that it was well tolerated across different dosing regimens. Its efficacy ranged from 62% to 90% depending on the dosage given, with an average of 70%, they said.

The results bode well for the near-term availability of a third vaccine to battle Covid-19, after a shot created by Moderna Inc. and one made jointly by Pfizer Inc. and Germany’s BioNTech SE were found to be more than 90% effective in their own late-stage trials. Pfizer and BioNTech last week said they had asked the U.S. Food and Drug Administration to permit use of their vaccine.


China and Russia have both deployed their own vaccines at home and overseas. Chinese authorities have inoculated nearly one million Chinese people with a vaccine from one state company, though it has yet to provide solid clinical evidence of its efficacy. Russia has said its own homegrown vaccine has an efficacy rate of above 90%.

AstraZeneca and Oxford’s vaccine stands out among the leading Western candidates. The partners committed to selling it without profit during the pandemic and promised to distribute it across a much wider geographic footprint, including in large parts of the developing world.

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The shot was created from a more traditional vaccine methodology than the gene-based technology used by Moderna and Pfizer. As such, it doesn’t need to be stored in subzero temperatures, making its rollout potentially easier.

AstraZeneca said it would seek emergency-use authorization from the World Health Organization to distribute the vaccine in low-income countries and prepare regulatory submissions to authorities in countries that have early-approval programs. A senior AstraZeneca executive said Friday the company hopes to have the two-dose shot available for use around year-end, pending regulatory approval.

The European Medicines Agency, which authorizes new medicines for sale in the European Union, said in early October that it had begun a rolling review of the Oxford vaccine to speed up a potential approval. A rolling review allows regulators to evaluate preliminary data such as those from lab experiments before final-stage clinical trials are completed.


Officials in the U.K., which is transitioning out of the EU, say they have the power to authorize use of a Covid-19 vaccine in the U.K. before year-end, if they choose. The U.K. also has been reviewing Oxford and AstraZeneca’s data on a rolling basis since early November. Canada has also begun a rolling review of the vaccine.

Trials of the vaccine, called AZD1222, were held in the U.K. and Brazil. Late-stage clinical trials of the vaccine are continuing in the U.S. following a trial pause there that spanned most of September and October. AstraZeneca wouldn’t likely apply for approval from the FDA until those trials have shown results.

The results released Monday were based on trials involving more than 23,000 participants. Individuals who received the vaccine received one of two combinations: a half dose followed by a full dose, which showed to be 90% effective; or two full doses, which showed to be 62% effective. Researchers said Monday the preliminary results are promising but will need to be fleshed out before scientists can understand why the half-dose regimen was more effective.

Oxford’s chief investigator in the trials, Prof. Andrew Pollard, said the results mean the vaccine “may be around 90% effective.” He said the regimen using a half dose for the first dose would also mean more people could be vaccinated with planned supplies.

As trials continue, Oxford and AstraZeneca will continue to refine the efficacy readings, helping determine whether the more-positive results hold up across a broader population of participants. The Oxford-AstraZeneca vaccine trials ultimately will enroll as many as 60,000 participants globally. The U.K. drugmaker said that the full analysis of the results is being submitted for peer review.


A full review of broader global trial results and full safety data are still to come.

Some researchers also said that it will be important to compare the effectiveness and safety of the leading vaccine candidates side by side.

AstraZeneca Chief Executive Pascal Soriot said the company is poised to make hundreds of millions of doses of the vaccine available upon regulatory approval.

A major question the researchers can’t yet answer is how long the positive effects of the vaccine last. That question for all eventual Covid-19 vaccines is key to understanding how long immunity might last, which will affect the required frequency of vaccination. It will also affect overall effectiveness in preventing the spread of the disease and helping jump-start stricken economies.

Oxford and AstraZeneca’s vaccine uses a more traditional approach than the Moderna and Pfizer shots, which both rely on a new technology called messenger RNA to induce an immune response inside the body. AstraZeneca’s vaccine instead relies on introducing a weakened, chimpanzee virus into the body to trigger the immune response.

“A particular strength of this vaccine is that it can be stored in a fridge,” said Prof. Azra Ghani, chair in infectious disease epidemiology at Imperial College London. “This means that it can be distributed around the world using existing delivery mechanisms.”

Oxford invented the vaccine along with a company spun out of the university called Vaccitech Ltd. In April, Vaccitech relinquished its rights to the vaccine to Oxford in exchange for a small slice of potential future royalties, enabling Oxford’s exclusive deal with AstraZeneca.


In May, Oxford started Phase 2 and 3 human trials, and AstraZeneca in late August launched a large, final-stage U.S. study aiming to enroll 30,000 volunteers to test the vaccine. The study was paused in early September after a patient in a U.K. trial suffered from an unexplained illness. The FDA permitted the U.S. study to resume Oct. 23. The separate, final-stage trial in the U.K. also paused but was restarted within less than a week.

An independent safety committee determined the illness was either unrelated to the vaccine, or couldn’t be linked to the vaccine because of a lack of information to determine a connection, according to an information sheet given to study volunteers and posted online by the University of Oxford.

Later, a participant in trials of the vaccine in Brazil died, but the country’s health regulator immediately said the trials would continue. At the time, Oxford said it had carried out an assessment of the case in Brazil and that there were no concerns about the safety of the trial. An independent assessment of the case didn’t present any concerns, AstraZeneca said.