Young people are at a greater risk from swine flu than the over-60s but are more reluctant to get vaccinated, an expert has warned.
Professor John Oxford, from Queen Mary, University of London, said pensioners would have been exposed to the virus in the 1940s and 1950s.
He explained older people are usually more vulnerable to flu in general but they have a tolerance to the swine flu strain.
Prof Oxford said: "That's the paradoxical thing. There were fewer deaths across those age groups compared to younger people last year.
"The only thing is, younger people can't be persuaded to have the vaccine."
Asked why fewer young people are getting inoculated, he said: "The problem is that on websites like Twitter people are saying we're all going to die from the vaccine, but that is utter nonsense."
The virologist said people should listen to expert advice, rather than rumours from unqualified sources on the internet.
An estimated 67.2% of over-65s and 41.5% of under-65s in at-risk groups have had the flu jab in England.
At-risk groups from the flu virus include people over 65, those suffering from a chronic heart or chest complaint, people with asthma, chronic kidney disease, diabetes, and those with lowered immunity due to cancer.
Figures out earlier this week revealed 17 people have died from flu so far this winter.
The Health Protection Agency (HPA) said 14 deaths were from swine flu and another three from flu type B.
All were under 65, with six deaths among children under 18.
At least eight of the 17 were in an "at-risk" group. None was pregnant and none had been vaccinated.
Prof Oxford said: "It's not a great start to the season, but it's a tricky virus to deal with. It's certainly not a walkover for people.
"I do expect trouble with it, but what came out from last year is that the vaccine was 95% effective."
Urging people to take preventative steps, he said: "The message here is, at this stage, we have to be very careful with it, but people can take action.
"We can't guarantee it's going to be 95% effective like last year, but certainly vulnerable people should get it now."
Amid fears a major flu crisis is brewing in the UK, the professor said: "We're quite well set in the UK."
As well as having enough flu vaccine to go round, he said there are "plentiful stocks of Tamiflu" which is taken shortly after symptoms of the virus start to take hold.
He said: "We're on full alert. People know what they're up to and what they are up against. I'd rather be here if anything goes wrong."
People should also take other precautions to avoid catching the virus, such as improving personal hygiene and avoid coming into contact with people suffering from flu.