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Britain on Wednesday seized on a new study that said the Oxford/AstraZeneca Covid vaccine significantly reduces virus transmission and is highly protective after a single dose, after stinging criticism about its effectiveness from EU leaders.
Health Secretary Matt Hancock said the research, which has yet to be peer-reviewed, vindicated its massive vaccination drive, which has so far seen some 10 million people receive a jab.
"It does show the world that the Oxford jab works, it works well," he told BBC radio. "It slows transmission by around two-thirds, so it categorically supports the strategy that we're undertaking."
The European Medicines Agency has recommended the Oxford/AstraZeneca jab for adults of all ages last week -- more than a month after independent regulators in the UK gave it the green light.
But several countries have advised against administering it to older people.
Germany said it will not advise over 65s to get it while Italy's medicines agency recommended alternatives for people aged over 55.
President Emmanuel Macron, who is under pressure for the slow roll-out of jabs across France, claimed the vaccine was "quasi-ineffective" for the over-65s.
But the vaccine developers refuted his claim, saying the uncertainty was driven by a lack of data in older age groups rather than any evidence that it did not work.
"From an immunological perspective, the older adults seem to respond in a very similar way to younger adults," Mene Pangalos, AstraZeneca's executive vice-president of biopharmaceuticals research and development, told a webinar Wednesday.
More data on older people should be available within weeks with the completion of a US trial and early results from Britain's vaccination drive, added Andrew Pollard, director of the Oxford Vaccine Group.
- Dosing schedule -
The study by Oxford University found that those who had been vaccinated with a single dose were 67 percent less likely to test positive with a PCR test, "suggesting the potential for a substantial reduction in transmission".
It also provided backing for the UK's strategy of administering as many first doses of vaccine to high-risk groups as possible and allowing a 12-week interval before the second dose, which has been criticised by some experts.
The other vaccine already being rolled out in the UK, the Pfizer/BioNTech jab, was designed to be administered with a shorter interval.
"We are confident that the 12-week dosing schedule is the right one for both of the vaccines that we're using in the UK," Hancock said Wednesday.
Researchers found that a single dose was 76 percent effective in preventing virus symptoms after 22 days and for up to 90 days, while it did not prevent asymptomatic illness.
It was more effective to wait 90 days than to administer the second dose, researchers found, "providing further support for current policy".
The survey covered 17,177 participants in Britain, Brazil and South Africa over the period up to December 7, 2020. None of the participants were hospitalised.
- Variant fears -
Britain has ordered some 100 million doses of the Oxford/AstraZeneca vaccine, which is cheap to make and being sold at cost price.
It can also be stored at fridge temperature, while the Pfizer/BioNTech vaccine requires extremely cold storage.
AstraZeneca hopes to have its "next-generation" vaccine, which will also target new mutations, ready by the end of this year, in time for winter, according to Pollard.
Britain has been one of the countries hardest hit by the pandemic, with more than 108,000 deaths from 3.8 million cases.
A highly transmissible variant strain forced another lockdown from early this month, with wide concern about the spread of a variation identified in Kent, southeast England, and another from South Africa.
Health officials this week began increased testing in eight areas across England where nearly a dozen cases of the variant were identified.
But opposition parties have criticised border controls, arguing they were not strict enough to stop the spread of new variants coming into the country.