Senior doctors are "deeply concerned" about the prospect of a major flu crisis this winter because the people who are most at risk are not coming forward for seasonal flu jabs.

An estimated 67 per cent of patients aged 65 or older, and 41.5 per cent of those aged 65 or under in the at-risk groups have received the vaccine so far this year – compared to nearly 70 per cent and 47 per cent last year. It is not clear why there has been a fall in take-up, but some doctors have blamed unfounded reports about the side effects of the swine flu vaccine. This year's vaccine protects against swine flu, which is circulating again, and other strains including flu type B.

The British Medical Association (BMA) wrote to the Government yesterday, urging it to step up its publicity campaign and warning that lower immunisation rates could mean the normal seasonal flu outbreak is much more serious. "Doctors are seeing high rates of influenza and have been telling us they are also seeing a lower uptake than usual for seasonal flu immunisation," said Dr Laurence Buckman, chairman of the BMA's GPs committee. "We strongly urge patients to make an appointment with their GP and get vaccinated."

Earlier this week, The Independent reported that 17 people had died from flu this winter. The Health Protection Agency (HPA) said 14 deaths were caused by swine flu and another three by type B flu. Of those who died, all were under 65, with six deaths among children under 18. At least eight of the 17 people were in an "at-risk" group, and none had been vaccinated.

Data also showed that the number of people seeking treatment from family doctors for flu-like illness has risen to 35 cases per 100,000, up from 13 in the previous week. The highest rates are among babies aged one to four and children aged five to 14.

The groups most at risk include people over 65, those with chronic heart or chest complaints, people with asthma, chronic kidney disease, diabetes or lowered immunity caused by cancer.

Professor Dame Sally Davies, the Chief Medical Officer for England, said yesterday: "It is particularly important for all pregnant women, no matter what stage they have reached in their pregnancy, to get the flu vaccine as soon as possible. This year, pregnant women are being offered the vaccine free of charge.

"Pregnant women are more likely to become seriously ill if they catch flu, which is why it is particularly important for them to get their jabs."

Dr Katie Laird, a senior lecturer in pharmaceutical microbiology at De Montfort University in Leicestershire, added: "Due to the nature of the flu virus – where mutations occur readily – it is difficult for the body's immune system to recognise the infection and can leave individuals such as the young, elderly, pregnant women and those with compromised immune systems without much natural immunity against the virus."