Dozens of practices have reported patients requesting private prescription or administration of a privately purchased vaccine, for themselves or their children.
The Medical Protection Society (MPS) has called for guidance to clarify whether GPs can administer privately-bought vaccines and how they should check its provenance and safety.
The MPS suggested patients may have bought vaccines after the DoH decided not to vaccinate children under five in this year's outbreak. Flu jab supply issues may have contributed.
RCGP immunisation lead Dr George Kassianos said: 'GPs are able to give the vaccine to patients not on their list, under a private contract. The vaccine used must be purchased privately.'
However, the MPS said there was 'nothing stopping' GPs from administering privately-purchased vaccine to any patient. But it warned GPs willing to do this to check the origin and safe storage of any such vaccine.
The MPS called for central guidance to clarify the issue.
It warned GPs must be aware of which services they can and cannot provide for patients to avoid falling foul of 'ethical or contractual obligations'.
MPS head of medical services Dr Nick Clements said: 'Definitive central guidance is needed to ensure consistency.'
The DoH and RCGP both claimed it was the other's responsibility to issue guidance.
Dr Pallavi Bradshaw, medico-legal adviser for the MPS, told GP: 'If any adverse outcomes occur, it's about ensuring there's a clear audit trail.'