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A trial is likely to be conducted in January to find out whether mixing and matching Covid vaccines provides better protection than two doses of the same, said the head of the British government task force.
Fast guide
How does the Pfizer / BioNTech Covid-19 vaccine work?
The Pfizer / BioNTech Covid vaccine is an mRNA vaccine. Essentially, mRNA is a molecule used by living cells to convert the sequences of genes in DNA into proteins that are the building blocks of all its fundamental structures. A segment of DNA is copied (“transcribed”) into a fragment of mRNA, which in turn is “read” by the cell’s tools to synthesize proteins.
In the case of an mRNA vaccine, the mRNA of the virus is injected into the muscle and our own cells read it and synthesize the viral protein. The immune system reacts to these proteins, which by themselves cannot cause disease, as if they had been transmitted by the entire virus. This generates a protective response that studies suggest lasts for some time.
The first two Covid-19 vaccines that announced the results of the three phase 3 trials were based on mRNA. They were the first to get out of the blocks because as soon as the genetic code for Sars-CoV-2 was known, it was published by the Chinese in January 2020, companies that had been working on this technology were able to start producing the mRNA. of the virus. Making conventional vaccines takes much longer.
Adam Finn, Professor of Pediatrics at the Bristol Children’s Vaccine Center, University of Bristol
The trial will begin if the Oxford University / AstraZeneca vaccine is approved in the coming weeks, as expected. Treatment can only be administered with licensed vaccines.
The news comes as the first British patients start receiving coronavirus vaccines from Tuesday, a coup carried out by Pfizer / BioNTech, a week after the UK became the first country in the Western world to approve a vaccine. Covid.
Those who participate in the January trial will receive an injection of the AstraZeneca vaccine and another from Pfizer. A vaccine from the American biotech firm Moderna will also be included if it gets approval.
The Pfizer and Moderna vaccines have been shown to be 95% effective in protecting people against the virus. For AstraZeneca, the efficacy was 62% among the largest cohort that received two doses, but increased to 90% among a smaller group that received half a dose initially, followed by a full dose.
Kate Bingham, outgoing chair of the UK Vaccines Task Force, said “mix-and-match” trials are not about pushing limited supplies of vaccines further. The UK government has ordered 40 million doses of the Pfizer vaccine and 100 million doses from the Oxford / AstraZeneca candidate.
“It’s not being done because of supplies,” Bingham said. “It has to do with trying to trigger the immune response and durability and nothing to do with the vaccines that we have.”
The concept is known as a heterologous prime mover. “It means mixing and matching vaccines,” Bingham said. “So you do a prime with one vaccine and then the second, be it 28 days or two months or whatever the agreed periods are, it would be with a different vaccine.”
Virus-based vaccines, such as the Oxford jab vaccine, which is based on the chimpanzee common cold virus, give a much higher cellular response, causing T cells to kill cells infected with the coronavirus. MRNA vaccines, like those from Pfizer, tend to elicit an increased antibody response. So the idea is to combine them, in any order, to help the immune system respond more powerfully to Sars-CoV2.
“No one has done it live and since we will have safe vaccines available, we should do that study, because then we will have the ability to produce better immune responses,” said Clive Dix, vice chair of the task force.
“It also has a small benefit, because if you prepare and push in any way at work, it can help with implementation, because it might be simpler to implement that way, but the main reason is to get a better immune response.”
Bingham and Dix spoke at the launch of a progress report on the working group’s first six months, which has secured deals for seven different vaccines for the UK.
Three of them, Oxford / AstraZeneca, Valneva and Novavax, are manufactured in the UK. The first doses of the AstraZeneca vaccine have been made in the Netherlands and Germany, but there are already 4 million doses in the country and most of the rest of the supply will be manufactured in the UK.
Questions remain as to when the Oxford / AstraZeneca vaccine will be approved. The government has asked the UK regulator to evaluate it after ongoing review, evaluating all data and information on safety and efficacy and product quality in recent months as it becomes available. But the full data from the late-stage clinical trials, involving 24,000 people, has yet to be published and it is not known how regulators will view the results.
Dix said the task force has no regrets in endorsing other types of vaccines in place of mRNA vaccines like those from Pfizer and Moderna, adding: “We certainly wouldn’t have had enough. [of the Pfizer vaccine] to vaccinate everyone. “
They looked at Moderna but realized they couldn’t get any doses until April, so they didn’t sign a contract. On the day Moderna reported its results, a deal was agreed to purchase 5 million doses, which was later increased to 7 million.
