Germany, one of the bloc's key players, on Tuesday threw its weight behind an EU export ban, as it announced strict virus measures would be imposed for five days over Easter to contain spiralling infections.
AstraZeneca had said Monday that stage three US trials had shown its vaccine was 79 percent effective at preventing the disease.
But in a late night release, the National Institute of Allergy and Infectious Diseases (NIAID) flagged concerns.
NIAID said a monitoring board "expressed concern that AstraZeneca may have included outdated information from that trial, which may have provided an incomplete view of the efficacy data."
"We urge the company to work with the DSMB (Data and Safety Monitoring Board) to review the efficacy data and ensure the most accurate, up-to-date efficacy data be made public as quickly as possible."
AstraZeneca 'problem'
Meanwhile, a spat is simmering between Britain and the EU over much-needed supplies of the AstraZeneca jab, which is cheaper and easier to store than many of its rivals.
European officials are furious that the Anglo-Swedish company has been able to deliver its UK contract in full while falling short on its supplies to the EU.
German leader Angela Merkel on Tuesday said, "We have a problem with AstraZeneca," as she backed an EU threat to ban AstraZeneca vaccines produced in the EU from being exported -- unless it delivers more of the 90 million doses it agreed to supply in the first quarter of 2021.
And public confidence in the drug has tumbled after several countries suspended its rollout because of isolated cases of blood clots.
A survey by British pollsters YouGov showed that a majority of people in the biggest EU states view the vaccine as unsafe.
The EU's medicines regulator and the WHO insist there is no evidence linking the drug to blood clots, and none was found in the large-scale trials in the US.
'We have a new virus'
Chancellor Merkel ordered the harsh nationwide shutdown, warning a potent strain of coronavirus was raging through the EU's most populous country.
"The situation is serious," she said. "Case numbers are rising exponentially and intensive care beds are filling up again."
A variant first identified in the United Kingdom has become the dominant strain circulating in Germany, the under-pressure leader said, adding that "we are in a new pandemic."
"Essentially, we have a new virus... it is much deadlier, much more infectious and infectious for much longer."
Cultural, leisure and sporting facilities will stay shuttered through to April 18, and a lockdown will come into force between April 1 and 5, as Christians celebrate Easter.
Almost all shops will be closed across the five days, and religious services will be moved online.
Banksy fundraiser
Britain on Tuesday marks the anniversary of its first coronavirus lockdown with a "National Day of Reflection," which will see parliament hold a minute's silence in tribute to the more than 126,000 people who have died.
The country ranks fifth in the world for both virus cases and deaths.
Prime Minister Boris Johnson said the last year has "taken a huge toll" and called the anniversary "an opportunity to reflect on the past year -- one of the most difficult in our country's history."
The country's state-run National Health Service (NHS) has been under huge strain, and on Tuesday a painting by UK street artist Banksy is expected to raise millions of pounds for health workers.
The artist left a note with the piece thanking hospital staff for their work battling the pandemic.
"Thanks for all you're doing. I hope this brightens up the place a bit, even if it's only in black and white," he wrote.
'Grotesque' vaccine gap
Globally, the coronavirus crisis that first emerged in China in December 2019 has killed more than 2.7 million people and infected over 123 million, according to official data collated by AFP.
Vaccination drives are seen as crucial to overcoming the pandemic and navigating countries out of brutal restrictions that continue to paralyse economies around the world.
More than 430 million jabs have now been administered, mostly in wealthier nations, and World Health Organization chief Tedros Adhanom Ghebreyesus has slammed the "grotesque" vaccine gap.
Papua New Guinea received its first batch of vaccines Tuesday as the impoverished Melanesian nation races to quell a Covid-19 surge overwhelming its fragile health system.
