Germany's vaccine committee has said AstraZeneca's Covid jab should only be given to people aged under 65.
The committee cited "insufficient data" for the effectiveness of the vaccine in those over 65, reports the BBC.
Efficacy studies for the AstraZeneca vaccine have so far been carried out on a small sample of the elderly population, EU regulators have said.
The European Medicines Agency is to decide on Friday whether to approve the vaccine for use across the EU.
The UK has been using the AstraZeneca vaccine in its mass immunisation programme for weeks now, and public health officials say the vaccine is safe and provides "high levels of protection" against Covid-19.
The news comes with the EU in dispute with leading manufacturers over a shortage of vaccines on the continent.
UK-based AstraZeneca has said production issues at its Europe-based plants mean it will be unable to deliver the promised number of doses to the bloc.
But the EU says the firm must honour its commitments and deliver the jabs by diverting stock from the UK. Pfizer-BioNTech has also cut the number of dozes it is delivering to the 27-member bloc.