More than a million people in England will receive an invitation to book their COVID-19 booster jab.
Texts will be sent out on Monday, while letters will be posted to those who are eligible for a third coronavirus vaccine dose later in the week, NHS England said.
Around 1.5 million people will be contacted and encouraged to use the National Booking Service.
Those eligible for booster jabs include those aged 50 and over, people living and working in care homes for the elderly and frontline health and social care workers.
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Booster shots will also be available to those who are clinically extremely vulnerable and anyone aged 16 to 65 in an at-risk group for COVID.
The Joint Committee on Vaccination and Immunisation (JCVI) said this week that people should receive their booster dose at least six months after they received their second COVID jab.
Scientists advising the government also urged people to get the Pfizer jab as a third dose, regardless of which jab they were initially administered.
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The JCVI also said half doses of the Moderna jab could be used as an alternative.
Health Secretary Sajid Javid said boosters will “strengthen the wall of defence” created by the vaccines.
He 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.”
Mr Javid said he urges everyone who receives a letter or text to get their jab “as soon as possible” in order to strengthen the wall of defence across the country.
Dr Nikki Kanani, GP and deputy lead for the COVID vaccination programme, said: “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.”
People who receive an invitation can book their appointment here, and those who cannot go online can instead call 119.
NHS England said millions of more invitations will be issued in the coming days and weeks.
Meanwhile, local health teams will prioritise care home residents and staff who are eligible and offer a booster jab by the beginning of November.