Booster jab invites will be sent out to more than a million people in England from next week to “strengthen the wall of defence” against Covid created by the vaccines.
People will receive texts from Monday (20 September), with letters to be sent to those who are eligible later in the week, NHS England said.
Some 1.5 million people will be contacted about booster jabs and encouraged to use the National Booking Service.
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Those eligible for boosters include anyone aged 50 and over, people living and working in care homes for the elderly, and frontline health and social care workers.
Those who are clinically extremely vulnerable and anyone aged 16 to 65 in an at-risk group for Covid will also be eligible for a jab.
The Joint Committee on Vaccination and Immunisation (JCVI) said people should receive their booster dose at least six months after they received their second Covd vaccine.
People who receive an invitation can book their appointment online. Those who cannot go online can instead call 119.
NHS England said millions more invitations are to be issued in the coming days and weeks.
Although there is a preference that people should get the Pfizer jab as a third dose, regardless of which jab they were initially given, the JCVI said half doses of the Moderna jab could be used as an alternative.
The NHS officially launched its Covid vaccine booster campaign on Thursday (16 September), with hospital hubs beginning to jab frontline health and care workers.
NHS England said local health teams will prioritise care home residents and staff who are eligible, and offer a booster jab by the beginning of November.
There are also booster campaigns in Wales, Scotland and Northern Ireland.
'Booster doses are an important way of keeping the virus under control for the long term'
Health and Social Care Secretary Sajid Javid said: “It is excellent that getting your booster jab has now become even easier thanks to the opening of the National Booking Service to those eligible.
“Booster doses are an important way of keeping the virus under control for the long term and will protect the most vulnerable through the winter months.
“I urge everyone who receives a letter or text to get their jab as soon as possible so we can strengthen the wall of defence across the country that each vaccine brings.”
Dr Nikki Kanani, GP and deputy lead for the Covid vaccination programme, added: “The NHS Covid vaccination programme has already prevented 24 million cases and saved more than 112,000 lives.
“As we head into winter we should not drop our guard so I would urge everyone to come forward and get a booster vaccination when they are invited.
“Getting a top-up vaccine is the best way to protect yourself and your loved ones from this cruel virus.”