Could combining Pfizer's and AZ's COVID-19 vaccines fill supply gaps? U.K. researchers aim to find out

The ability to mix and match vaccines from different companies could help address supply shortfalls, University of Oxford researchers argue. (Getty Images)

Given that the COVID-19 vaccines from Pfizer and AstraZeneca each require one dose, followed a few weeks later by a booster shot, could the two products be used interchangeably?

That’s the question researchers from the Oxford Vaccine Group have set out to answer with a new clinical trial designed to address a mounting problem: The demand for COVID vaccination in many locales around the world is far outstripping the supply.

Oxford’s 13-month study will recruit more than 800 volunteers in England, who will receive one of four different combinations of the vaccines. Half the participants will get two doses of the same vaccine, while the others will receive one dose of either the Pfizer or AstraZeneca vaccine, followed by a booster of the other company’s product.

The researchers will use blood samples taken at various intervals to monitor patients’ immune responses, while also recording any adverse reactions that occur. They believe the data they collect will help policymakers decide whether they can adopt mix-and-match strategies to address supply shortfalls and other logistical challenges, as well as the changing nature of the COVID-19 virus.

“If we do show that these vaccines can be used interchangeably in the same schedule this will greatly increase the flexibility of vaccine delivery, and could provide clues as to how to increase the breadth of protection against new virus strains,” said chief investigator Matthew Snape, associate professor at the University of Oxford, in a statement. AstraZeneca is partnered with Oxford in developing its shot.

“There are no data available on the interchangeability of Pfizer-BioNTech’s vaccine (BNT162b2) with other COVID-19 vaccines to complete the vaccination course,” a Pfizer spokesperson said in an emailed statement, adding that anyone who already received one dose of its vaccine should get the same shot as a booster.

AstraZeneca did not immediately respond to a request for comment from Fierce Pharma.

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The Oxford trial is launching just days after AstraZeneca proposed a solution of its own to address the vaccine supply constraints. Last week, CEO Pascal Soriot told reporters that the European authorization of his company’s vaccine specifies that the booster shot can be given as long as 12 weeks after the initial dose.

In fact, data released earlier this week showed that when people received the second shot of AstraZeneca’s vaccine 12 weeks after the first, the efficacy rate was 82.4%, versus 54.9% in those who got the booster within six weeks.

Soriot suggested the data supported a strategy of using all available doses of AstraZeneca’s vaccine and not stockpiling any booster shots because the company should be able to fill any supply gaps within 12 weeks.

Pfizer and BioNTech, meanwhile, have brought in some support to ramp up the production of its mRNA vaccine. Last month, Novartis agreed to produce the Pfizer/BioNTech COVID shot at one of its Swiss manufacturing facilities starting in the second quarter. Deliveries of the vaccines produced there should start in the third quarter, Novartis said. That deal followed a similar agreement with French drugmaker Sanofi, which also has separate development deals with GlaxoSmithKline and Translate Bio.

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Pfizer’s vaccine uses mRNA technology, while AstraZeneca’s is a modified viral vector, so the Oxford team hopes the new trial will also provide some clues as to how a combination of the two technologies might work against fast-spreading mutant strains of COVID-19.

Many COVID vaccine makers have launched their own investigations to try to determine just how effective their shots are against the new variants. Pfizer scientists, working with a team at the University of Texas, released a study showing the company’s vaccine could neutralize an engineered version of the mutant virus spreading through the U.K. and South Africa

But not everyone is convinced the data are conclusive. Evercore ISI told its clients last week that Pfizer’s analysis failed to include some of the mutations found in the South Africa coronavirus variant, making it a less-than-comprehensive study. SVB Leerink analysts griped that vaccine makers are testing their products against the new variants with assays that have not been adequately validated.

AstraZeneca isn’t taking any chances with the newly emerging COVID-19 strains. It is now working with Oxford to develop a next-generation version of its vaccine that’s designed to neutralize new variants and that could be available next fall, an executive said during a press briefing, according to Reuters.