For the first time, a nasal spray vaccine is being offered to all 2 and 3 year-old children because they are key "spreaders" of the virus.
Children with long-term health conditions and pregnant women are among those known to be at risk with around 800 people admitted to intensive care with flu last year.
Prof Dame Sally Davies, chief medical officer, said being protected against flu was vital for certain groups of people.
"Severe winter flu and its complications can make people really ill and can kill - you are eleven times more likely to die from flu if you are in a clinical at-risk group.
"I urge everyone who is eligible to get the vaccine and help protect themselves and their families this winter."
The new campaign follows research which found that young children's close contact with each other means they are more likely to transmit the virus to other vulnerable people, such as babies and elderly people.
The national flu vaccination programme should eventually include annual vaccination of all two- to 16-year-olds.
At present the government says it would not be effective for the NHS to vaccinate every healthy person against flu. However people can still pay for the flu vaccine at their local pharmacy.
Dr Paul Cosford, medical director and director for health protection at PHE, highlighted how flu was unpleasant for the majority of people but could be life-threatening for others.
"It can be very serious for older people and those groups at risk of developing complications including people with weakened immune systems, as well as those with underlying conditions such as neurological disorders, liver, lung or renal disease, heart problems or diabetes, and pregnant women.
"Vaccination remains the best way to protect against the potential serious harm from flu this winter."