Many people who risk becoming seriously ill if they get the flu have not yet been vaccinated against it.
The number of pensioners who have received the vaccination has fallen from the same period last year. And the number of other "at-risk" patients, who are under the age of 65 and suffer from various medical complications, has also decreased.
Figures show that by the end of last week, 48.9% of patients aged 65 or older had the flu jab, but in the same week in 2011, 54.8% of pensioners had received it.
Similarly, 28.7% of patients with other medical complications, including asthma, heart disease, liver disease and diabetes, had been vaccinated by October 28, while at the same point in the previous year, 32.2% of patients in England had already been given the jab, according to Department of Health figures.
For most people, flu is an unpleasant illness but it is not serious, but certain people are at greater risk of developing complications of flu, such as bronchitis and pneumonia.
Around 4,700 people die every year in England after getting flu, a Department of Health spokeswoman said. People in at-risk groups are 11 times more likely to die than someone who is not in an at-risk group.
Health officials are launching a campaign to encourage at-risk groups to get vaccinated. A new website, called Winterwatch, is also being launched later this month which will provide the latest winter-related health data.
Health Secretary Jeremy Hunt said: "Cold weather can be hazardous for our health - particularly for older people and those with respiratory illnesses.
"Each year, the cold weather is responsible for an increase in deaths and thousands of cases of flu, falls, heart attacks and strokes. In past years, these extra pressures have cost the NHS £42 million in emergency admissions alone.
"As winter approaches, we should all be on our guard against health problems - by taking simple steps and looking after our older friends and family we can keep warm and well."