Take up of the flu jab has dropped which is a worry when more people can get the flu and spread it about not realizing how dangerous infections are for people with a bad chest.
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, as has the number of other "at risk" patients who are under the age of 65 and suffer from various medical conditions.
By the end of last week, 48.9% of patients in England aged 65 or older had had the flu jab, while in the same week in 2011, the take-up was 54.8%.
Similarly, 28.7% of patients with ailments including asthma, heart disease, liver disease and diabetes had been vaccinated by 28 October, while at the same point last year 32.2% of patients had been given the jab, according to Department of Health figures.
For most people, flu is unpleasant but not serious. Those suffering from ailments such as bronchitis and pneumonia are at greater risk of developing complications. 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 those outside the category.
Health officials are encouraging at-risk people to get vaccinated. A website called Winterwatch is also being introduced this month to provide the latest winter-related health data.
The 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."
Public health minister Anna Soubry said: "We have taken the decision this year to run a flu campaign because too many people in at-risk groups have not come forward for the jab yet, although local campaigns have been running for the past month.
"Our campaign aims to encourage people who are most at risk from flu, who have put it off or who don't think it is important, to get the vaccine."
David Salisbury, director of immunisation, said: "You are 11 times more likely to die from flu if you are pregnant or have a serious health condition, and each year thousands of people die after catching flu.
"That's why we are reminding people who are particularly vulnerable to the consequences of flu to get the vaccine.
"Severe weather can be dangerous for vulnerable groups such as older people and those with serious illnesses."
Clare Cox, spokeswoman for the British Lung Foundation, said: "Flu is unpleasant for anyone who catches it, but for particular at-risk groups, such as older people and those with respiratory conditions, the effects can be particularly serious.
"Getting vaccinated against flu can help protect against unnecessary illness and is free for these at-risk groups, so along with digging out your gloves and scarfs, we would strongly advise that people contact their GP about a flu vaccination as part of their normal preparations for winter."