Doctors are expected to ration this year's flu jabs for the next two months because of a delay in supplying vaccine after a glitch at laboratories earlier in the year.

High-risk groups including the elderly and those with respiratory conditions will be prioritised more rigorously than usual until medical suppliers catch up with the government's order for 15.2m doses, probably in late December.

Deliveries to GPs' surgeries are likely to be 1.5m doses behind last year's total of 10.5m doses in place at the end of October. The Department of Health said the outlook had improved since June, when officials warned that surgeries might need to share stocks, but asked doctors to choose "wisely" which patients to treat first. The interruption to supply follows a problem common to all manufacturers which had to switch vaccines after their initial choice to combat this winter's flu, vaccine Wisconsin 161, failed to grow. A second strain, 161B, has been successful but production of the huge quantities required is well behind schedule.

David Salisbury, director of immunisation at the Department of Health, said local flu coordinators would be on hand to prevent "famine or feast" hiccups in vaccine distribution. He said: "We want doctors to be sure that they are using their vaccine wisely so that people who have got clear risk factors are the ones they are bringing in first, according to a priority list we sent out earlier this year."

The high priority categories of patient are those aged 65 and over, sufferers from chronic respiratory disease such as asthma, chronic heart, renal or liver disease, diabetes, victims of a compromised immune system and those living in long-stay residential care homes or similar facilities.

Dr Salisbury warned there was no guarantee that everyone needing a vaccine would get one in October, the recommended month for effective treatment. He said: "Practices that were late putting in their orders are not going to be at the front end of the queue in getting their deliveries. Some people will have to wait but there will be a vaccine for them eventually."

The delay follows complaints last year that priority patients missed out early on in the autumn because of a rush for vaccine by the "worried well". This year's order was more than a million units higher than in 2005-06 to try to meet any repeat surge in demand.

By the end of last December vaccines had been given to 75.3% of 65 and overs, the highest rate to date. Priority cases aged under 65 reached 50% coverage - a figure the Department of Health has targeted for a major rise.

Hamish Meldrum, chairman of the British Medical Association's GPs committee, said doctors were hoping for a late start to this winter's flu. He said: "It will be quite a challenge for surgeries to immunise all their at-risk patients before the winter flu season sets in. There certainly won't be spare supplies to provide jabs for those not in the at-risk groups. It really will help us if patients follow the adage 'Don't ring us, we'll contact you'."

Lorna Layward, research manager at Help the Aged, said: "The government needs to act urgently to ensure that the most vulnerable people get their vaccinations early in order to prevent unnecessary deaths." Diabetes and asthma care groups also called for a firm timetable for priority groups.

The shadow health secretary, Andrew Lansley, said he would ask the health secretary, Patricia Hewitt, today to issue guidance to GPs on how to protect their patients "if a flu epidemic strikes and we do not have enough vaccines available".

Winter conditions are blamed for 20,000 deaths annually in Britain, rising to 40,000 in particularly cold years. More are attributed to flu than any other cause.

FAQ

Who is offered a flu jab?

The over-65s and those with chronic conditions, such as heart or lung diseases or a depleted immune system.

Who else?

People who live in residential homes or long-stay facilities, where flu will spread quickly. Carers and healthcare workers are also offered the jab.

What is the timetable for delivering vaccines to doctors?

By the end of October GPs will have received more than 9m doses, and a total of 13m by the end of November. The full delivery of 15.2m doses should be complete by the end of December.

Who decides how the vaccines are made?

The World Health Organisation monitors the spread of the virus across the world and decides which three strains need to be included in the vaccine for the next flu season.