Hundreds of thousands of people asked to shield in England are being invited for a Covid-19 vaccine jab.

About 1.7 million more people were added to the shielding list last week after experts identified additional adults at serious risk of the virus.

Some 600,000 of that group are now being invited to book a slot at a vaccination centre or pharmacy service, NHS England said.

Hard-working NHS staff have already protected more than 15 million of the most vulnerable people against Covid in a matter of weeks

The remainder have already had their jab in the first phase of the vaccination programme.

Letters are also arriving for about 445,000 people aged 64 who have not yet been vaccinated.

The shielding list was expanded after scientists developed a new tool which assesses whether someone is at risk of severe disease or death.

The tool looks at multiple factors including age, ethnicity, body mass index, other health conditions and also postcode, which is indicative of levels of deprivation.

The predictive risk model was developed by researchers led by scientists at Oxford University.

The additional 1.7 million brought the number on the shielding list to almost four million.

Meanwhile, a further 10 vaccination sites, including Reading’s Madejski stadium and a theatre in Basildon, come online this week.

Those who receive letters can book online or call 119 free of charge anytime between 7am and 11pm seven days a week.

People can pick a slot at 100 vaccination centres or almost 200 pharmacy services.

Professor Stephen Powis, NHS medical director, said: “The NHS vaccination programme is the biggest in the health service’s history and continues to go from strength to strength.

“Hard-working NHS staff have already protected more than 15 million of the most vulnerable people against Covid in a matter of weeks.

“However, if you have already been offered a jab, especially if you’re aged 70 or over, but have not taken it up, it is not too late. Please come forward so the NHS can protect you against coronavirus immediately.”

Vaccine minister, Nadhim Zahawi, said: “The vaccination programme continues to expand at pace, and I encourage everyone, regardless of your religion or background, to come forward and get your vaccine when it’s your turn.

“Vaccines will protect you and those around you from this awful disease and are the best way out of this pandemic.”