Several major EU countries halted the AstraZeneca jab Monday over blood clot fears, as the World Health Organization and Europe's medicines watchdog insisted it was safe to use.
Both organisations will hold special meetings this week after a host of countries said they would stop using the vaccine pending further review.
The fresh suspensions were a major blow to a global immunisation campaign that experts hope will help end a year-long pandemic that has already killed over 2.6 million people and decimated the global economy.
Germany, Italy, France and Spain all said Monday they were pausing use of the jab, after Ireland and the Netherlands announced similar measures over the weekend.
And Indonesia also said it would delay the rollout of the jab, which is cheaper than its competitors and was billed as the vaccination of choice for many poorer nations.
But the WHO insisted countries should keep using the vaccine, adding that it had scheduled a meeting of its experts on Tuesday to discuss the vaccine's safety.
"We do not want people to panic and we would, for the time being, recommend that countries continue vaccinating with AstraZeneca," WHO chief scientist Soumya Swaminathan said.
"So far, we do not find an association between these events and the vaccine."
Several countries have reported feared links between the vaccine and blood clots, despite repeated assurances of its safety.
The European Medicines Agency (EMA) -- which is holding a special meeting on Thursday -- echoed the WHO's calls for calm, and said it was better to get the vaccine than not.
"The benefits of the AstraZeneca vaccine in preventing Covid-19, with its associated risk of hospitalisation and death, outweigh the risks of side effects," the agency said in a statement Monday.
As controversy around the vaccine swirled, in Italy any hope that the pandemic was reaching its endgame was dampened as schools, restaurants, shops and museums closed in several cities.
The streets of central Rome were quiet on Monday morning and businesses already battered by a year of anti-virus measures braced for another hit.
"I'm staying open because I'm selling cigarettes, otherwise it would not be worth it," said Rome coffee shop owner Carlo Lucia.
"It's just a waste of money."
Meanwhile, intensive care doctors in Germany issued an urgent appeal for new restrictions to avoid a third wave as the British variant takes hold there.
And while France was hoping to avoid another national lockdown, the economic toll of the pandemic was laid bare in poverty-struck Marseille, where unemployment is on the rise.
"Often I don't sleep at night, I wonder what will happen the next day," 52-year-old Edith Ferrari, who struggles to survive between short-term contracts, told AFP.
"My hope in 2021 is to have a work contract but with Covid," she added, her voice trailing off.
More than 350 million vaccines have now been administered globally, with the AstraZeneca jab among just a handful approved for use around the world.
The European Union has approved four jabs so far, and is monitoring others -- including Russia's Sputnik V vaccine.
The Russian developers said on Monday they had reached production agreements in key European countries.
The news came as the WHO said it had raised nearly $250 million in the past year from individual donors and companies towards battling the pandemic.
WHO chief Tedros Adhanom Ghebreyesus said the fund's success proved "what we can accomplish together in times of need".
More than a year after his organisation declared the coronavirus threat a pandemic, a much-anticipated report on the origins of Covid-19 is expected to be released this week.
The report follows a fact-finding mission of international experts assembled by the WHO, which travelled in January to the Chinese city of Wuhan where the virus first emerged in December 2019.
"Within the next few years, we're going to have real significant data on where this came from and how it emerged," said British zoologist Peter Daszak, one of the team members.