The coronavirus vaccine developed in Britain by Oxford University and UK-Swedish pharmaceutical firm AstraZeneca has suffered several setbacks since its development, dampening hopes over its global role in ending the pandemic.
Doubts have been heightened after South Africa suspended the start of its inoculation programme using the jab this week, following research it had failed to prevent mild and moderate cases of a virus variant there.
The shot was already under scrutiny about its efficacy for over-65s, after several European countries restricted its use to younger adults only, despite approval from the EU medicines agency for all ages.
In a sign of the mixed-messaging, French President Emmanuel Macron said at the end of January the vaccine was "quasi-ineffective for people over 65".
Many poorer nations around the world are relying on the logistical advantages offered by the AstraZeneca-Oxford vaccine, which does not require ultra-low storage conditions.
In Britain, where more than 12 million jabs have been given as part of the country's biggest ever vaccination drive, it has been administered alongside the Pfizer-BioNTech shot.
Prime Minister Boris Johnson on Monday sought to reassure the millions of Britons already given the AstraZeneca-Oxford vaccine, telling reporters UK officials believe both jabs were "effective in combating serious disease and death against all variants".
Scientists were getting "ever faster and more expert" to come up with "variants of the vaccines" to adapt to the evolving situation, he added.
'Minimal protection'
The University of Witwatersrand, Johannesburg, which conducted the trial that has prompted the latest concerns, reported Sunday that it only "provides minimal protection against mild-moderate Covid-19 infection" from the South African variant.
However, AstraZeneca noted none of the 2,000 participants developed serious symptoms and reiterated its belief that the vaccine will still protect against severe disease.
Peter English, a former head of the British Medical Association's public health medicine committee, agreed "what matters most is preventing more serious forms of Covid-19" and that more extensive trials involving the South African strain were still needed.
"It is by no means clear if it is more or less effective against the variant than other vaccines," he added.
In Britain, Oxford University said Friday researchers had found its jab had "similar efficacy" against a more contagious variant that first emerged in September and has become the dominant form of coronavirus across the country.
The news was welcomed in Britain, where some 113,000 people have died during the pandemic, and where vaccines are seen as a way out of the crisis.
"We are ready to protect our most vulnerable and stay a step ahead of the virus, whatever it throws at us," vaccines minister Nadhim Zahawi wrote Monday in the Daily Telegraph.
Work was under way to tweak approved vaccines to protect against new variants, he said.
"While it is right and necessary to prepare for the deployment of an updated vaccine, we can take confidence from the current roll out and the protection it will provide all of us against this terrible disease," he added.
'Easily redesigned'
A host of European countries appear unconvinced by the more limited existing evidence on the AstraZeneca-Oxford jab's effectiveness among over-65s.
France, Germany, Spain, Greece, the Netherlands, Belgium, Denmark, Sweden and Romania have all placed limits on its use for certain segments of their elderly populations.
The restrictions follow a row between AstraZeneca and the EU last month, after the pharma giant said it could not fulfil its promised initial deliveries due to production problems.
Its vaccine is central to the first wave of distribution of Covax, the global vaccine procurement and distribution pool for poorer nations.
Many low-income countries are relying entirely on it to start immunising their most vulnerable populations, but cannot receive their first doses until the World Health Organization (WHO) grants emergency authorisation.
Its experts were set to decide Monday on their usage recommendations.
Some 145 countries are set to receive 337.2 million doses, but nearly all of those -- 336 million -- are AstraZeneca vials.
Despite the doubts, scientists in Britain remain confident the vaccine, or an updated version of it, can live up to early expectations.
"Vaccines that are effective against the more severe forms of disease may not affect milder forms, so there is optimism that severe disease will still be prevented," said Peter Openshaw, experimental medicine professor at Imperial College London.
"In addition, many of the vaccines now proven to be effective can be relatively easily redesigned to express emerging forms of the viral protein."
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)
