A vaccine marked with a test tube is seen in front of the AstraZeneca logo in this illustration, September 9, 2020.
Dat Ruvic | Reuters
British health officials on Wednesday approved the AstraZeneca and Oxford Covid-19 shots, but also rejected one of their central claims: that half a dose followed by a standard dose provides more protection against infection.
The re-evaluation of the best vaccine dosing regimen was an unexpected move by the UK Medicines Authority on the basis of its own analysis of as yet unpublished data and raised new questions about the effectiveness of a vaccine that has not yet been approved in the UK. other countries. .
Although cheaper and easier to distribute than rival photos, the Oxford / AstraZeneca vaccine has been affected by uncertainty about the most effective dose since data published last month showed that half a dose followed by a full dose had a rate 90% success, while two complete photos were 62% effective.
Researchers at Oxford said the more successful result was an “interesting result” that deserved further testing.
A Reuters investigation found, however, that the existence of the low-dose / standard dose arm was the result of a miscalculation of potency by Oxford researchers, calling into question the robustness of the result.
Munir Pirmohamed, chairman of a British advisory group on Covid-19 vaccines, validated those doubts on Wednesday, saying the 90% efficacy rate did not remain under analysis.
Instead, Pirmohamed said a higher success rate may be due to a larger gap between the administration of the first and second blows.
“The low-dose / standard dose regimen, although cited to be 90% effective, is confused by the fact that the interval between the first and second doses was quite long,” Pirmohamed said in a conference call. the press.
“And we think this result may be related to that range, rather than the dose itself,” he said.
Wei Shen Lim, the Covid-19 vaccine chair in the UK, said a single dose of Oxford / AstraZeneca vaccine was about 70% effective within 21 days of a second dose.
Pirmohamed said leaving the three-month gap rather than the one-month gap between doses could raise the success rate of the AstraZeneca / Oxford vaccine to 80 percent.
After British health officials revealed new details about the vaccine’s effectiveness, an AstraZeneca spokesman said: “It is the responsibility of regulators to authorize how the vaccine should be used.”
Factors that will be considered include the comparable immunogenic response after two doses with any of the regimens, as well as protection against severe disease (100%), he said.
“We believe we have the best vaccination strategy approved by the MHRA.”
A “winning formula”
Faced with a record increase in infections caused by a highly contagious variant of the virus, the UK gives priority to receiving a first dose of vaccine in as many people as possible rather than taking a second dose. Delaying the distribution of two photos would help expand the offer.
The UK Medicines and Medicines Regulatory Agency (MHRA) has recommended a 4-12 week interval between doses of AstraZeneca / Oxford vaccine and has updated its guide to a second dose of Pfizer-BioNTech vaccine, saying it could be administered within 12 weeks, rather than the 21 days initially recommended.
Hundreds of thousands of Britons have already received their first dose of the Pfizer vaccine after the UK was the first country to approve its launch, with the second dose to be released this week.
Pfizer seemed cautious about the prospect of changing the second dose schedule, noting that it had not been evaluated on different dosing schedules.
“There is no evidence that protection after the first dose is sustained after 21 days,” the statement said, adding that the implementation of alternative programs should be closely monitored.
While decisions about alternative dosing regimens are up to the health authorities, Pfizer believes it is essential … to ensure that each beneficiary has the maximum possible protection, which means immunization with two doses of vaccine.
AstraZeneca CEO Pascal Soriot was quoted in the British Sunday Times as saying that his company has a “winning formula” to compete with the approximately 95% efficacy rates of vaccines developed by Pfizer and Moderna. He said he could not say more pending the release of the new data.
Speaking to Sky News, Oxford vaccine developer Sarah Gilbert said there was transparency in the process.
“The MHRA said it would publish its evaluation report. There are different groups in the process, we had different intervals between doses and different dose levels, as you say, and that makes the analysis somewhat complicated,” she said. said.
“The MHRA has done its own analysis and they are very confident that they will now authorize the vaccine for emergency use.”
Oxford did not respond to a request for comment following the MHRA briefing.
Regulators in other countries have taken a more cautious approach than the UK, and the various efficacy rates cited by the MHRA, as well as its new recommendations on the timing of secondary doses, have led scientists to request the release of the details behind its approval.
“More needs to be known, as many points about these decisions remain unclear. The MHRA and JCVI have promised to provide more information urgently,” said Saad Shakir, director of the Drug Safety Research Unit near Southampton.
Jeremy Farrar, director of the Wellcome Foundation for Health Research, said a new study may be needed to provide clearer data on the optimal timing of a second dose.
“We will also need to continue to monitor and improve our understanding of how long the protection lasts and whether they can prevent transmission,” he said.
This would be best achieved by a randomized study of the timing of the second dose.