Global health experts were under increasing pressure to clear up questions over the safety of AstraZeneca's COVID-19 shot on Tuesday, as Sweden and Latvia joined countries suspending their use in a further blow to Europe's vaccination rollout.
A World Health Organization (WHO) committee of experts was reviewing isolated cases of bleeding, blood clots and low platelet counts in people vaccinated and was in dialogue with the European Medicines Agency (EMA), which was also meeting.
The EMA would hold a news conference at 1300 GMT and the WHO committee may also issue a statement on Tuesday, spokespeople for the EU executive and the U.N. health agency said.
The European Union's largest members - Germany, France and Italy - suspended use of AstraZeneca's vaccine on Monday pending the outcome of an investigation into the reports.
The addition of Sweden and Latvia on Tuesday brought to more than a dozen the number of EU countries to act since reports first emerged of thromboembolisms affecting people after they got the AstraZeneca shot.
The WHO and EMA had earlier joined AstraZeneca in saying there is no proven link, but some experts said rare cases of highly unusual cerebral thrombosis in younger people did appear to indicate a causal link to the AstraZenica shot.
"The benefits of vaccination significantly outweigh the risks, especially for the elderly," said Karl Lauterbach, health spokesman for Germany's Social Democratic Party.
"But it could be the case that the risks of the vaccine are higher for certain patient groups such as young women. It is possible that the EMA will issue specific warnings," he told Deutschlandfunk radio in an interview.
European epidemiologists remained baffled that similar cases had not occurred in unusual numbers in Britain, which began using AstraZeneca earlier and has administered more than 10 million doses.
"These symptoms have not yet been observed there," said Stephan Becker, head of the Institute for Virology at Philipps University Marburg.
"This is a very unfortunate situation, but if there is such a suspicion, then it must be investigated and vaccination must be stopped for that time."
In the EU's largest member states, including Germany, France, Italy, the Netherlands and Spain, AstraZeneca has accounted for about 13-15% of shots administered since the rollout started almost three months ago, with Pfizer-BioNTech making up the majority, according to officail EU data.
Nicola Magrini, the director general of Italy's medicines authority AIFA, told daily la Repubblica in an interview that the choice to suspend the AstraZeneca shot was "political".
He said it was safe and said its benefit to risk ratio was "widely positive". There have been eight deaths and four cases of serious side-effects in Italy following vaccinations, he added.
Governments say they acted out of an abundance of caution but the move deprives them of vitally-needed doses to step up vaccination campaigns that have got off to a slow start due to scarce supply.
AstraZeneca said last week it would try to deliver 30 million doses to the European Union by the end of March, down from a contractual obligation of 90 million and a previous pledge made last month to deliver 40 million doses.
Still, the European Commission said on Tuesday it expects to receive more than 200 million doses of COVID-19 vaccine from Pfizer PFE.N and BioNTech 22UAy.DE in the second quarter, putting the EU on course to meet its inoculation target.
The EU aims to vaccinate at least 255 million people, or 70% of its adult population, by the end of the summer. The bloc has administered 11 shots so far for every 100 residents, while Israel - a world leader in vaccination - has given 108 doses, according to Our World in Data.
At the same time a third wave of infection, driven by more infectious viral variants, threatens to worsen Europe's year-old coronavirus pandemic that has claimed 575,000 lives and further delay recovery from a pandemic economic slump.
Deutsche Bank on Tuesday slashed 2021 economic growth forecasts for the euro area by a whole percentage point, citing spillover of the ongoing pandemic-linked activity restrictions.
Sources said Germany had no choice but to act after its vaccine watchdog identified an unusual number of cases of rare cerebral vein thrombosis. Of 1.6 million people in Germany who had got AstraZeneca, seven fell ill and three died.
Yet the risk of dying of COVID is still orders of magnitude greater, especially among those most vulnerable such as the elderly, said Dirk Brockmann, an epidemiologist at the Robert Koch Institute for infectious diseases.
"One is probably 100,000 times more likely to die of COVID than because of an AstraZeneca vaccine," Brockmann told ARD public television.