A number of GP surgeries across Lincolnshire have been forced to postpone their flu jab programmes due to shortages of the vaccine.
Crucell, a pharmaceutical company based in the Netherlands, has suspended delivery of all supplies of its flu vaccine because of 'an unexpected test result'.
The company supplies 10% of the UK's flu vaccine stocks and the shortages are affecting a number of flu programmes in the county.
Glebe Surgeries in Saxilby and Skellingthorpe, near Lincoln, have only been able to supply half the vaccinations they normally provide.
Practice Manager, Reg Tompkins said: "We've done 1,000 vaccinations so far but usually do just under 2,000 a year.
"We order stocks from two companies and basically, company A provided and company B did not."
A spokesman for Crucell said that supplies had been halted voluntarily by the company because of patient safety concerns following an unexpected test result on one batch.
It did not say what this result was.
Further tests are being conducted to investigate the cause before any further batches of vaccine are released.
Lincolnshire NHS reassured patients that they will receive their flu jabs and reminded only a small proportion of the UK supply has been affected.
An NHS spokesperson said: “Affected practices are liaising directly with the supplier to ensure that this delay causes minimal disruption to flu vaccination clinics.
“As a result, some flu vaccination clinics have been rescheduled and patients will be informed of the dates and times for future flu clinics at their local GP surgery."
Flu affects millions of people every winter and particular people in certain high-risk groups are encouraged to receive vaccination in the Autumn.
Those considered high-risk are the over-65s, pregnant women, children and those with respiratory conditions.