The Oxford-AstraZeneca COVID-19 vaccine shows 62% to 90% efficacy

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The AstraZeneca logo at the pharmaceutical company's factory in Dunkirk, France. Photo by: Raphael Lafargue / Abaca Press

MANILA — Interim analysis of the University of Oxford and AstraZeneca’s novel coronavirus vaccine candidate shows it’s highly effective in preventing COVID-19, but differences in efficacy rates for different dosing regimens of the vaccine require further review, experts have said.  

The Oxford-AstraZeneca vaccine showed 62% efficacy in preventing COVID-19 in participants given two full shots of the vaccine. However, the efficacy rose to 90% when the vaccine was given at only half dose during the first shot, followed by a full dose for the second shot. When combining these two, the efficacy rate of the vaccine is at 70.4%, according to a news release.

This has created confusion among journalists and experts, who are hoping to gain access to the full data in the coming weeks.

“While we are cautiously optimistic about the data … the press release by AstraZeneca is not sufficient to draw definite conclusions. Full transparency of the clinical trial data and analysis is needed before conclusions on the vaccine’s efficacy and utility can be made,” said Dr. Manuel Martin, medical innovation and access policy adviser at Médecins Sans Frontières’ Access Campaign, in response to Devex.

Dr. Jerome Kim, director general of the International Vaccine Institute in South Korea, shared the same views.

“It is exciting to see another COVID-19 vaccine, the chimpanzee adenovirus vaccine from Oxford/AstraZeneca, show efficacy of 70% against COVID-19. The vaccine has features that may make it more practical than the RNA [ribonucleic acid] vaccines, but questions around the dose and the differences in efficacy between the two dose groups await an opportunity for full data review,” he told Devex over email.

Accessibility concerns about promising Pfizer, BioNTech COVID-19 vaccine

Experts have welcomed interim efficacy data from the ongoing phase 3 clinical trial of Pfizer and BioNTech's COVID-19 vaccine candidate, but concerns around affordability and access remain.

The interim analysis came from the vaccine’s phase 3 trials involving over 20,000 volunteers from the United Kingdom, Brazil, and South Africa. Over 3,000 of the participants received the half dose plus full dose vaccine regimen, professor Andrew Pollard, chief investigator of the Oxford Vaccine Trial, said in a news briefing on Monday.

University of Oxford’s professor of vaccinology Sarah Gilbert, who has been involved in the vaccine’s development from the start, said they will be digging into details in the coming weeks as to why results show better efficacy at the half dose plus full dose regimen.

A separate trial of the vaccine is ongoing in the United States, but it does not include an arm with the half dose plus full dose vaccine regimen. Mene Pangalos, executive vice president of biopharmaceuticals research and development at AstraZeneca, said they hope to share the latest data to regulators in the United States this week.

Pam Cheng, executive vice president for global operations and IT at AstraZeneca, said the results would mean having more available vaccine doses to deploy, once the vaccine receives regulatory approvals. "We've got capability to be able to supply up to 3 billion doses" in 2021 globally, Cheng said.

The latest data follow results from two other COVID-19 vaccine candidates in the past few weeks. Initial results from Pfizer and BioNTech, and Moderna showed their vaccine candidates — both messenger-RNA-based vaccines — were both more than 90% effective in preventing COVID-19. Pfizer last week said final results from its trials showed 95% effectiveness of its vaccine candidate.

Clarity over the efficacy of the Oxford-AstraZeneca vaccine is crucial, given some of its potential advantages when it comes to projected production worldwide and distribution.

“The vaccine has features that may make it more practical than the RNA [ribonucleic acid] vaccines, but questions around the dose and the differences in efficacy between the two dose groups await an opportunity for full data review.”

— Dr. Jerome Kim, director general, International Vaccine Institute

A critical issue with both Pfizer-BioNtech and Moderna’s vaccines however is their cold chain requirements. Both need to be stored at extremely low temperatures, whereas the Oxford-AstraZeneca vaccine can be stored at 2-8 degrees Celsius, or at fridge temperatures, allowing for easier transport and distribution.

Still, IVI’s Kim said administration of a half dose plus full dose vaccine regimen “could be confusing in large vaccination campaigns (simplicity is always better).”

The Oxford-AstraZeneca vaccine is also one of the few vaccines that have been made available to the COVAX Facility. It has the “highest projected production capacity worldwide” and has a “relatively geographically diverse distribution of manufacturers,” including the Serum Institute of India, MSF’s Martin said.

However, there remains a question regarding the vaccine’s affordability in the long-term, according to Martin. AstraZeneca has said it won’t profit off the vaccine during the COVID-19 pandemic, but there are questions on which party makes that determination, or what happens after that.

Still, both Oxford researchers and officials from AstraZeneca are encouraged by the interim results, not only of their vaccine candidate, but of others too.

“It was a very big day for the world a couple of weeks ago, when we got the first announcement of a SARS-CoV-2 vaccine with high efficacy. That really changed the field for the rest of us working on vaccine development, because it showed that it could be done,” Gilbert said, during the same press briefing.

Meanwhile, Pascal Soriot, CEO at AstraZeneca said there is “no competition.”

“Sometimes people think there is a competition. But if you add the capacity that Pfizer has announced, plus the Moderna-announced capacity, plus our capacity, which is much bigger, the three of us don't even have enough vaccine production for the world,” he said.

About the author

  • Jenny Lei Ravelo

    Jenny Lei Ravelo is a Devex Senior Reporter based in Manila. She covers global health, with a particular focus on the World Health Organization, and other development and humanitarian aid trends in Asia Pacific. Prior to Devex, she wrote for ABS-CBN, one of the largest broadcasting networks in the Philippines, and was a copy editor for various international scientific journals. She received her journalism degree from the University of Santo Tomas.