A second coronavirus vaccine manufacturer has warned of supply issues, frustrating European Union efforts to distribute the jab.
UK drug-maker AstraZeneca said a production issue meant initial volumes would be lower than anticipated.
The European Commission said it was trying to obtain more information.
This comes on top of a halt to vaccinations in some parts of Europe due to a cut in deliveries of the Pfizer-BioNTech vaccine.
AstraZeneca, which developed its vaccine with Oxford University, disclosed the situation in a statement, but gave few details.
"Initial volumes will be lower than originally anticipated due to reduced yields at a manufacturing site within our European supply chain," it said.
Reuters news agency quotes an unnamed EU official as saying that the company had told the EU that the supply would reduce to 31 million - a cut of 60 percent - the number of doses it could deliver to the bloc in the first quarter of this year.
Unlike the Pfizer-BioNTech and Moderna vaccines, Astra-Zeneca's product is yet to be approved by the EU's drug regulator, though this is expected at the end of this month.
AstraZeneca has signed a deal with the EU to provide at least 300 million doses of its vaccine.
Austrian media have reported that only 600,000 of two million AstraZeneca doses promised by the end of March will arrive in the country on time, with the remaining 1.4m now being delivered in April.
A delay would be "completely unacceptable", Austrian Health Minister Rudolf Anschober said.
Threats of legal actions
As for Pfizer, the US firm said it had to cut shipments for the next few weeks while it worked to increase capacity at its Belgian processing plant. The EU has ordered 600 million doses from Pfizer.
The Pfizer cuts have forced Germany's most populous state, North-Rhine Westphalia, and several regions in Italy to suspend first jabs. Vaccinations for medics in Madrid have been halted too.
Italy and Poland have threatened to take legal action in response to the reduction in vaccines.
Meanwhile, cases in many European countries are surging. Germany has reached 50,000 Covid deaths and Spain has seen record infections in recent weeks.
Hungary's government, which has complained at slow EU approval of the Oxford-AstraZeneca vaccine, has reached a deal with Russia to buy up large quantities of the Sputnik V vaccine, even though it has not received EU approval.
How Europe has been hit by vaccine delays
Italy has been told to expect a a 20 percent cut in the Pfizer-BioNTech vaccine next week - it has already seen a 29 percent dip this week - and Rome is considering legal action. Some Italian regions have seen a 60 percent fall in doses.
Germany, where BioNTech is based, has had several states struggle with vaccine deliveries. North Rhine-Westphalia, in the west, halted jabs in hospitals on Tuesday and paused first vaccinations in nursing homes too. Second vaccinations are continuing but special centres for the over-80s will not open now until next month.
Authorities in and around the Spanish capital Madrid have temporarily stopped vaccinating healthcare personnel this week, saying they had only received half the doses they were expecting. The national government is rationing distribution until Pfizer's deliveries improve. Spain reported a record 44,357 cases in one day on Thursday.
Romania has warned that its vaccine stocks could be down to almost zero by the end of the first week of February. The Czech government has warned that the reduction in distribution has created "huge complications".
Poland, which began by vaccinating healthcare workers and moved to care homes this week, saw a 50 percent drop in the number of vaccines delivered this week. Ministers say they have been promised normal service by mid-February. If that is not the case, Warsaw says it would consider legal action.
France requires negative test for arrivals
EU leaders agreed late on Thursday to keep their internal borders open but warned that restricting non-essential travel may be needed to curb the spread of the virus.
France has said it will impose tighter travel restrictions for European arrivals from Sunday night, requiring a negative PCR test within three days of travel. Health Minister Olivier Véran has appealed to people to stop using home-made fabric masks - health officials are recommending that medical masks are worn instead.
Belgium is to ban non-essential travel for Belgian residents from late January to 1 March, other than for people living in border areas to go shopping. Anyone making an "essential" trip that lasts more than 48 hours will have to self-isolate and take two Covid tests after they return.
Denmark, meanwhile, is suspending flights from the UAE for five days because of a tip-off suggesting that pre-flight tests are unreliable. Denmark requires all air passengers to have tests taken in the 24 hours before a flight.
The total number of German Covid deaths climbed above 50,000 on Friday, but the number of infections has fallen in the past week. Leading virologist Christian Drosten has warned Germans that as increasing numbers get vaccinated there will be growing pressure to curb restrictions. "Then we won't be talking in terms of 20,000 or 30,000 infections a day but in the worst case scenario 100,000," he told Spiegel magazine.
- BBC