"A trial is likely to go ahead in January to find out whether mixing and matching Covid vaccines gives better protection than two doses of the same one, the head of the British government’s taskforce has said."
"Those who take part in January’s trial will get one shot of AstraZeneca’s vaccine and one of the Pfizer injection. A vaccine from US biotech firm Moderna will also be included if it gets approval.
Pfizer’s and Moderna’s vaccines have both been shown to have 95% efficacy at protecting people against the virus. For AstraZeneca’s, efficacy was 62% among the largest cohort given two doses, but rose to 90% among a smaller group given half a dose initially, followed by a full dose.
Kate Bingham, outgoing chair of the UK’s vaccine taskforce, said the “mix and match” trials were not about making limited supplies of the vaccines go further. The UK government has ordered 40m doses of the Pfizer vaccine and 100m of Oxford/AstraZeneca’s candidate.
“It’s not being done because of supplies,” said Bingham. “It’s to do with trying to trigger the immune response and the durability and nothing to do with what vaccines we’ve got.”
The concept is known as a heterologous prime-boost. “It means mix and matching vaccines,” said Bingham. “So you do a prime with one vaccine and then the second – whether it’s 28 days or two months or whatever the agreed periods would be – would be with a different vaccine.”
Viral-based vaccines such as the Oxford jab, which is based on a chimp common cold virus, give a much greater cellular response – prompting the T-cells to kill cells infected with the coronavirus. The mRNA vaccines, like Pfizer’s, tend to generate a bigger antibody response. So the idea is to combine them, in whichever order, to help the immune system respond more powerfully to Sars-CoV2.
“No one’s ever done it live and since we’ll have safe vaccines available we should do that study, because then we have the ability to actually produce better immune responses,” said Clive Dix, deputy chair of the taskforce.
“There is a slight benefit to it, too, in that if prime and boosting either way around work, it may help with the deployment, because it might just be simpler to deploy that way round, but the main reason is to get a stronger immune response.”
Bingham and Dix were speaking at the launch of a progress report on the first six months of the taskforce, which has secured deals for seven different vaccines for the UK."
Pilot planned for January will give subjects a shot of both Oxford/AstraZeneca and Pfizer/BioNTech versions
www.theguardian.com