Why the AstraZeneca-Oxford Covid-19 vaccine is different

AstraZeneca and the University of Oxford say their vaccine is up to 90 percent effective. But there’s a lot we still don’t know.

If someone told you in March, when the World Health Organization finally called the Covid-19 outbreak a pandemic, that we’d have three strong coronavirus vaccine candidates by mid-November, you might have called that person delusional.

Yet with Monday’s news from AstraZeneca and University of Oxford that early results from their phase 3 trial demonstrate their vaccine’s effectiveness, that’s exactly the scenario we’re in.

In a press release, the pharmaceutical giant and its Oxford co-developers reported interim findings from two of their ongoing trials — one in the UK and one in Brazil. The trials used different approaches to inoculating the more than 11,000 people who participated, and found two levels of efficacy, which they averaged to 70 percent. The researchers also found no severe cases or hospitalizations in the study participants who got the vaccine.

Lisa Maree Williams/Getty Images

In the UK trial, the vaccine — known as AZD1222, or ChAdOx1 nCoV-19 — was given as a half dose, followed by a full dose around one month later, resulting in 90 percent efficacy. In the Brazil group, study participants were given two full doses at least one month apart, and the efficacy was 62 percent.

The researchers aren’t sure why there was this striking gap in vaccine performance but said in a press conference that the half dose may better prime the immune system to respond to the second full vaccine.

“These findings show that we have an effective vaccine that will save many lives,” said Andrew Pollard, chief investigator of the trial at the University of Oxford.

Either way, 50 percent efficacy is the floor set by the US Food and Drug Administration and the European Medicines Agency (the FDA equivalent in Europe) for approval. The AstraZeneca-Oxford research team will “immediately” submit their efficacy and safety findings to regulatory agencies around the world, seeking early approval.

While the efficacy outcome falls short of the 95 percent preliminary result recently reported by both Moderna and Pfizer/BioNTech, the result is still very promising. At around $3 to $4 per dose, the AstraZeneca-Oxford shot is also the cheapest of the three options and should be easier to distribute globally (since it can be stored in regular refrigerators). That’s why lower-income countries around the world have been pre-purchasing access.

AstraZeneca said the company has the capacity to supply 3 billion doses of the vaccine in 2021.

But, as with all the promising new coronavirus vaccine candidates, there are some caveats to consider. And since the results came via press release and lacked detailed data, they raise questions we don’t yet have answers to. Here’s the rundown.

The Oxford-AstraZeneca vaccine could be a game changer for low- and middle-income countries

Among the Covid-19 vaccines furthest along in development, the AstraZeneca-Oxford candidate is most likely to be affordable to low- and middle-income countries. And considering much of the world’s population currently lives in low- and middle-income settings, it’s the shot that, if effective, is poised to make the biggest dent in the pandemic worldwide.

It uses a novel approach to inoculation, but one that’s different from Pfizer-BioNTech and Moderna — and from conventional vaccines.

In the past, vaccine makers typically used the virus itself or a fragment of the virus, often in a weakened or inactivated form, to inoculate recipients. But the new generation of vaccines use genetic instructions for making parts of the SARS-CoV-2 virus, the pathogen that causes Covid-19. All three candidates —Pfizer, Moderna, and AstraZeneca-Oxford — deliver the instructions for making the SARS-CoV-2 spike protein, or the part of the virus that lets it enter human cells to begin with. And it’s these instructions that are injected, which human cells then use to manufacture parts of the virus, in essence coaching the immune system to fight off the invader should it arrive.

The Moderna and Pfizer-BioNTech vaccines both use mRNA as their platform for delivering the genetic instructions. AztraZeneca-Oxford uses DNA instead, and the DNA is delivered to cells with the help of another virus known as an adenovirus. (Other Covid-19 vaccine developers, like CanSino Biologics and Johnson & Johnson, are also using adenovirus vectors.)

AstraZeneca, unlike Moderna and Pfizer/BioNTech, has promised to sell its shot at cost — around $3 to $4 — and not to profit from the vaccine while the pandemic is ongoing. According to the FT, that price is “a fraction” of the expense of the other vaccine candidates, which are expected to cost between $15 and $25 per dose.

Also unlike the two other leading vaccine candidates, it doesn’t require extremely cold temperatures for storage.

That’s the distribution hurdle Moderna and Pfizer-BioNTech are working to overcome. Moderna’s vaccine requires long-term storage at minus 20 degrees Celsius (minus 4 degrees Fahrenheit) and is stable for 30 days at refrigerator temperatures between 2 and 8 degrees Celsius (36 to 46 degrees Fahrenheit). Meanwhile, the Pfizer-BioNTech vaccine demands ultra-cold temperatures of minus 70 degrees Celsius (minus 94 degrees Fahrenheit) or lower, with about five days of shelf life at refrigerator temperatures.

The AstraZeneca-Oxford vaccine, however, can be stored in a normal refrigerator for at least six months.

That’s why the AstraZeneca-Oxford vaccine has become the leading contender lower-income countries are relying on to end their epidemics. According to Bloomberg, the shot “accounts for more than 40% of the supplies” going to low- and middle-income countries.

“[T]he vaccine’s simple supply chain and our no-profit pledge and commitment to broad, equitable and timely access means it will be affordable and globally available supplying hundreds of millions of doses on approval,” said Pascal Soriot, CEO of AstraZeneca, in a statement.

But the US is also poised to benefit. In May, the Biomedical Advanced Research and Development Authority (BARDA) under the Department of Health and Human Services pledged up to $1.2 billion to back the AstraZeneca-Oxford vaccine, aiming to secure 300 million doses for the US. In total, the company is aiming to supply 3 billion doses of the vaccine around the world.

Now, some caveats

The AstraZeneca-Oxford results so far came via press release and gloss over the details we’d need to really understand how the vaccine truly works in people. AstraZeneca-Oxford also released fewer details than the other two companies, and reported their results in a way that made drawing comparisons among the three candidates difficult. Let’s go over what we know.

• Before clinical trials begin, research groups are supposed to set out a plan for how they’ll run the studies and analyze and share the results. That helps ensure experimenters don’t move the goalposts. So researchers are questioning why AstraZeneca-Oxford apparently deviated from that plan. In particular, they made their announcement today based on combined results of two different trials rather than parsing several of their clinical trials separately, as originally promised, according to meta-scientist Hilda Bastian.

• We don’t have the details of what side effects the study participants experienced. The company only reported there were no serious safety events confirmed to date, and that the vaccine “was well tolerated across both dosing regimens.” We do know that the UK trial for AZD1222 was paused in July and again in September after two volunteers reported neurological problems. Investigations later found no link between the vaccine and these symptoms, and regulators allowed the trial to resume in October.
• While we know the number of participants included in the analysis of each of the two groups, (2,741 in the UK versus 8,895 in Brazil), we don’t know how many got the vaccine versus the placebo, which raised a statistical question about how many people were infected with the virus in the group that saw 90 percent efficacy. Some statisticians have suggested the number may be very small — and potentially unreliable:

• The press releases also lack details about the demographics of people participating in the trials. AstraZeneca said its trial participants come from “diverse racial and geographic groups who are healthy or have stable underlying medical conditions,” but without knowing the exact numbers, it’s hard to gauge how well they reflected the groups most at risk of severe disease (including older adults and people of color).
• The trials also didn’t use a simple placebo to measure efficacy. In the UK arm of the trial, volunteers were randomly assigned to receive the AZD1222 vaccine or the meningococcal vaccine, MenACWY. In the Brazil arm, the comparison group was given MenACWY for the first dose and a saline placebo for the second dose.
• Another factor to consider: AztraZeneca-Oxford measured their results in a different way from their two major competitors. The Moderna and Pfizer/BioNTech trials only captured Covid-19 infections in their trial pool that advanced far enough to produce symptoms, while the AstraZeneca trials conducted weekly swab tests among their participants, allowing them to detect much less severe cases — including potential asymptomatic infections — among their volunteers. These differences make it a trickier to draw apples-to-apples comparisons of the efficacy of the different vaccines.

Together, these factors highlight that there’s still a lot to learn about the new vaccines, even as they’re set to roll out imminently. The Moderna, Pfizer-BioNTech, and Oxford-AstraZeneca teams have all vowed to publish their trial results in peer-reviewed journals. But distribution on a limited emergency use basis may begin as soon as next month, pending approval from regulators.

Still, it’s worth pausing over how remarkable it is that there are now three SARS-CoV-2 vaccine candidates that have reported high levels of efficacy, and all of them use a technology that has never been deployed at a large scale in humans before.

For now, AstraZeneca-Oxford, Moderna, and Pfizer-BioNTech still need to complete their trials, and regulatory submissions, for full approval. But if they pass regulators, the coronavirus vaccines may be the beginning of an entirely new approach to inoculating people against disease.