Hundreds of thousands of people will be asked to bring their second Covid-19 vaccine forward, the NHS has announced.
More than 650,000 people will receive messages via text this week to ensure their second jab is eight weeks after the first.
It is said to be as part of a drive to boost vaccinations before Covid restricts are lifted on Monday.
Initial guidance from vaccination experts said people should receive their Covid-19 vaccines up to 12 weeks apart.
A longer delay helped to boost immunity while enabling the constrained vaccine supply earlier in the year to get to more people.
But the Joint Committee on Vaccination and Immunisation has since changed its stance to say people should get their second dose eight weeks to 12 weeks later.
Now the NHS is calling people forward to make sure they get their second dose eight weeks after their first.
When some people booked their vaccine appointments they will have booked the second jab 12 weeks later, but now they are being asked to rebook for a closer date.
Sir Keith Willett, head of the Covid-19 vaccination programme in England, said: “Thanks to the hard work of NHS staff and volunteers up and down the country, almost two thirds of people in England have already received two doses of the jab.
“The crucial second dose gives maximum protection against the virus and it will protect you, your family and those around you.
“As we approach July 19, there has never been a more important time to get jabbed and it has never been easier – from pop-up sites in the community to walk in centres, NHS staff are going to great lengths to ensure vaccines are as convenient as possible.
“So I urge everyone to bring their second-dose appointment forward to eight weeks as soon as they can.”
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Health Secretary Sajid Javid said: “Getting that vital second jab will also allow us to return to doing the things we missed, such as going on holiday. Everyone should take up the opportunity as soon as they can so we can all start to enjoy the freedoms we’ve missed.”
Text invitations appear as an alert from “NHSvaccine” and include a web link to the NHS website to reserve an appointment.
People who cannot go online can call the service on 119 instead to book their jab.
It comes after vaccination experts concluded there was “no gain” in bringing the interval between doses forward even further still.
As infections rise, vaccination experts assessed whether there could be benefit from bringing the second dose forward from eight weeks to four weeks.
But they decided there is no short or long-term gain by shortening the interval.
On Wednesday, Professor Anthony Harnden, deputy chair of the JCVI, told Times Radio: “We’ve looked at this data very carefully over the last few days and it is quite clear from the AstraZeneca vaccine, there is absolutely no doubt that the longer interval gives you much better protection.
“But we concentrated on the Pfizer vaccine because of course that’s one that’s been given to younger people at the moment.
“And it’s quite clear from antibody T-cells studies that you get much lower response, and poorer quality memory response with the shorter interval – that’s a four-week interval compared to an eight-to-12-week interval.
“And the actual real data vaccine effectiveness studies show that there is a lower vaccine efficacy against symptomatic disease with shorter intervals compared to longer intervals.
“Then we got the modellers to look at this and actually, the number of infections will rise if we reduce the dose.”