Britain's biggest supplier of influenza vaccines said on Saturday it was postponing deliveries due to a Brexit-related shortage of lorry drivers, delaying the government's winter inoculation campaign.
Medics say the campaign offering free flu vaccines to more than 35 million people is even more important this year, after lockdowns for the coronavirus pandemic suppressed the circulation of flu last year.
The medical supplier Seqirus confirmed delays of up to two weeks in England and Wales, blaming "unforeseen challenges linked with road freight delays".
Britain has for weeks been grappling with a shortage of lorry drivers, after a post-Brexit exodus of drivers from the European Union. The pandemic has also caused a large backlog of tests for new UK drivers.
The National Health Service (NHS) has started inviting those eligible for a free flu jab to book an appointment from this month, but Seqirus instructed practitioners to wait for certainty on its supplies.
The development comes after NHS doctors were forced to cancel routine blood tests due to a shortage of test tubes.
"That this appears to be stemming from similar issues around freight capacity and transportation is incredibly concerning, and we must ask the government exactly what it is doing to urgently address this," said Richard Vautrey of the British Medical Association.
The winter flu campaign is set to be the biggest yet in Britain, targeting all secondary school students and adults over 50, among others.
There was no immediate official comment but a senior member of the Joint Committee on Vaccination and Immunisation, which advises the government on inoculations including for Covid-19 and flu, expressed concern.
"Clearly influenza immunisation this year is really important and the reason it's so important is because of lockdowns, we've had very low circulating influenza levels last winter," Professor Anthony Harnden told BBC television.
"So it's really important to get the influenza immunisation and really important to get it as soon as possible."