A mass swine flu immunisation programme got under way today with the country's chief medic urging all priority groups to take up the offer of vaccination.
Sir Liam Donaldson, chief medical officer for England, said it was important for frontline health and social care workers to get themselves vaccinated against swine flu along with other groups classified as a "priority" or at risk.
He said: "This is the first pandemic for which we have had vaccine to protect people.
"I urge everyone in the priority groups to have the vaccine - it will help prevent people in clinical risk groups from getting swine flu and the complications that may arise from it.
"It's important for frontline health and social care workers to have the vaccine.
"It will help prevent them and their families getting the virus from patients, it will stop them passing the virus on to their patients, it will potentially protect them from mutated strains and it will reduce the disruption to NHS services caused by people being absent due to illness."
Sir Liam's call comes amid concern about the effects of a possible postal strike on the vaccination programme.
GPs will begin receiving deliveries of the vaccine from Monday and will send appointment letters to patients classified as at risk.
Sir Liam told BBC Breakfast: "We are a little bit worried about the postal strike because GPs send their letters out, letters of appointment, so we are working very hard to try and get round that, ensuring that people get their appointments in time."
Asked how they would get appointment letters to people if a strike goes ahead, he said: "By bundling the mail up and ensuring that it is delivered because some mail will still be delivered for urgent situations, so we are going to try and sort out that little glitch - which isn't a particularly welcome thing to happen in the middle of having this vaccine."
Professor Stephen Field, president of the Royal College of General Practitioners, described the planned postal strike as "extremely unhelpful".
He told GMTV: "In the short term - if it's only for a day or two - we will manage but what will happen is we won't be able to get to people consistently and it will also mess up the system because we will be planning to bring people in in sequence, so we could do without that.
"But we will get hold of patients because they are local."
The immunisation programme offering more than 11 million people the vaccine began with hospitals vaccinating frontline health care workers and their patients who fall into at risk categories against swine flu.
Around two million frontline health and social care workers will be offered the vaccine, as they are classified as at increased risk of infection and of transmitting the infection to susceptible patients.
The vaccination programme will be extended over the coming weeks.
The Department of Health said at-risk groups will be given priority in the following order: people aged over six months and under 65 years in current seasonal flu vaccine clinical at-risk groups; all pregnant women; household contacts of people with compromised immune systems; and people aged 65 and over in the current seasonal flu vaccine clinical at-risk groups.
The Department of Health said this did not include otherwise healthy over-65s, since they appeared to have some natural immunity to the virus.
Patients will be contacted by their GPs if they fall into one of the at-risk categories, the Department said.
The GSK vaccine Pandemrix will be offered to the "vast majority", with most people needing only one dose of this vaccine for protection.
The campaign comes after Sir Liam announced last week in his weekly briefing that the number of deaths of people in the UK suffering from swine flu has passed 100.
Health Protection Agency estimates released last Thursday showed about 370,000 people have contracted the virus so far in the UK.
Health Secretary Andy Burnham, who was visiting University College Hospital in London to launch the campaign today, said: "Our best line of defence against swine flu is the vaccine.
"I'm very pleased to say that the UK is one of the first countries in the world to start vaccinating against this virus.
"The independent committee of experts in the UK has recommended that all those in the at-risk groups should be offered the swine flu vaccine.
"It is also being offered to frontline health and social care workers to protect them and their patients and ensure the NHS is staffed, should it come under pressure this winter."