Germany has said it will not recommend the Oxford-AstraZeneca coronavirus vaccine for people aged 65 and over.
Scientists in the UK - where the vaccine is being given as part of a mass immunisation programme - stand by their decision to give it to the over-65s.
Why is Germany limiting its use of the vaccine?
Germany says it will only offer the vaccine to 18-64 year olds because there was not enough data on how it affected the over-65s.
AstraZeneca has been open about the fact that in the early stages, only 10% of the people recruited to test the vaccine's effectiveness were 65 or older. However, trials on this age group are currently running in several different countries.
The vaccine has been shown to be safe and older people appear to have a strong immune response to the vaccine. After receiving the shots, their blood has plenty of the required antibodies that can fight coronavirus.
The company says its clinical trial data "supports efficacy in the over-65s age group". Public Health England said the company's data on the vaccine's immune responses was "very reassuring".
The European Medicines Agency is expected to make a decision on whether to approve the vaccine this week .
How does the Oxford vaccine work?
It is made from a weakened version of a common cold virus (known as an adenovirus) from chimpanzees. It has been modified to look more like coronavirus - although it can't cause illness.
When the vaccine is injected into a patient, it prompts the immune system to start making antibodies and primes it to attack any coronavirus infection.
Research has shown it is highly effective . No one given the vaccine in trials developed severe Covid or needed hospital treatment.
Unlike Pfizer's jab - which has to be kept at an extremely cold temperature (-70C) - the Oxford vaccine can be stored in a normal fridge. This makes it much easier to distribute.