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Volunteers are being sought for a first global trial to establish the efficacy of giving people a first dose of one vaccine and a second dose of a different vaccine.
The trial, which is run by Oxford University and funded by the government’s Vaccine Task Force, has been described by ministers as “of enormous importance.”
It will recruit 820 people over the age of 50 who have not yet received a vaccine, to receive a first dose of the Oxford / AstraZeneca vaccine or the Pfizer / BioNTech vaccine. Then some people will receive an alternative vaccine at a second appointment within 12 weeks, and others will receive the same vaccine again.
Public Health England’s Green Book on Vaccines already tells the NHS that in exceptional circumstances, if people arrive for their second dose and the vaccine they originally had is not available, they may receive a different one.
Scientists want to know if the protection of the vaccine mix is the same, reduced, or even better, compared to sticking to the same vaccine at all times.
With the constant supply of vaccines always in question, the researchers said the information they collect would be useful not just for the UK but for the whole world.
There is also the possibility that giving an individual two different vaccines in a row could provide greater protection against the more infectious variants of Covid that have emerged in the UK, South Africa and Brazil.
“If we show that these vaccines can be used interchangeably in the same program, this will greatly increase the flexibility of vaccine delivery and could provide clues on how to increase the breadth of protection against new virus strains,” said Matthew Snape , an associate professor of pediatrics and vaccinology at the University of Oxford and the trial’s principal investigator.
In a briefing, Snape said there was evidence from mouse studies that combining an adenoviral vector vaccine, such as the Oxford jab, with an mRNA vaccine, such as Pfizer / BioNTech, could elicit a better response.
Both vaccines, and the Novovax and Janssen vaccines, which are likely to be added to the trial if approved, target the spike protein of the virus. “So I think we do anticipate that it will generate a good immune response with these combinations, but first we have to test it, we have to see,” he said.
Volunteers, who will be recruited through the NHS Vaccine Research Volunteer website, will have their blood drawn to measure antibody build-up after vaccination against the virus. Some will receive their second dose after four weeks, and some after a 12-week interval, to provide more data on the government’s policy to widen the dose gap.
Professor Jonathan Van-Tam, England’s deputy chief medical officer and principal lead of the study, said: “Given the inevitable challenges of immunizing large numbers of the population against Covid-19 and potential global supply limitations, there are definite advantages to have data that can support a more flexible immunization program, if needed and if approved by the drug regulator.
“It is also possible that combining vaccines can improve the immune response, giving even higher levels of antibodies that last longer. Unless this is evaluated in a clinical trial, we just won’t know. This study will give us a better idea of how we can use vaccines to stay aware of this nasty disease. “
Nadhim Zahawi, the minister for the deployment of the Covid-19 vaccine, called it “a clinical trial of enormous importance that will provide us with more vital evidence on the safety of these vaccines when used in different ways.”
He said mixing vaccines would not be recommended outside of the study “until the researchers and the regulator are absolutely confident that the approach is safe and effective.”
