Letters to 850,000 people aged 56 to 59 have begun landing on doorsteps across England.
The latest invites have been sent after more than eight in ten people aged 65 to 69 took up the offer of a jab.
NHS staff have vaccinated more than 560,000 people across Lancashire and South Cumbria, meaning more than one-third of the adult population, have already received the life-saving jab.
Jane Scattergood, director of nursing and quality for the Fylde Coast CCGs and COVID-19 vaccination director for Lancashire and South Cumbria, said: “The NHS vaccine programme is committed to protecting the country against coronavirus and it is testament to our incredible staff and partners that we can now move on to the next age group.
“We must not forget that our success in vaccinating more than half a million people is down to careful planning and the hard work of those staff, our partners and our communities who have come forward for vaccination when called.
“The vaccines are both safe and effective, so if anybody who is eligible but hasn’t been vaccinated yet, I’d urge them to go online or call 119 and get themselves booked in.”
People receiving the letters are invited to go online to the national booking service to arrange a jab at a time and location that is convenient for them. If they are not able to go online, they can call 119 free of charge.
The NHS is vaccinating in line with JCVI guidance which sees people invited to be vaccinated in order of risk, which increases with age and people aged between 50 and 55 are set to be invited shortly.
Health and Care Secretary Matt Hancock said: “The NHS vaccination programme is in full swing and more than 21 million of the most at-risk people have already received their first dose. This includes more than 90% of those aged 65 and over and almost nine in 10 people who are clinically extremely vulnerable. It is an extraordinary feat and we remain on track to offer a first vaccine to all adults by 31 July.
“We are now inviting people aged 56 to 59 to get their jabs and I urge everyone eligible to come forward as soon as possible.”
Vaccinations are now being administered at more than 1,600 sites across the country, including Fylde Coast sites at Blackpool Winter Gardens, AFC Fylde and more, with the distribution of centres meaning 98% of the country lives within 10 miles of at least one vaccination service.
People can use the national booking service to reserve a slot at an NHS Vaccination Centre or one of the pharmacy-led services across the country.
Appointments are staggered to allow for social distancing and people are being asked not to turn up early to avoid creating queues.
Everyone will receive a health status check and a pre-vaccination assessment before they have their jab.
The NHS made history when Maggie Keenan became the first person in the world to be protected against coronavirus outside of a clinical trial when she received the Pfizer vaccine at Coventry Hospital on 8 December.
The NHS was also the first health system to deliver the new Oxford/AstraZeneca coronavirus vaccine when Brian Pinker, 82, received his on 4 January.