London, March 15 : British charities have urged millions of vulnerable people with underlying health conditions across the UK to book their coronavirus vaccine jabs, local media reported Sunday. Charities including Cancer Research UK, Mencap and the Terrence Higgins Trust have written an open letter on Sunday to those in priority group six, including those aged 16 to 64 with an underlying health conditions such as cancer, diabetes and heart disease, Xinhua news agency reported. "The good news is, even if you have not received your letter yet, you can now get an appointment at a vaccination centre or community pharmacy, quickly and easily, by using the national booking system or calling 119 in England," the 18 charities said in the letter. According to the British Department of Health and Social Care, more than half of the 7 million people in that group have had their first dose. The National Health Service (NHS) will send about 2 million text messages in England asking those in group six to book an appointment at a vaccination center or pharmacy. More than 23.6 million people in Britain have been given the first jab of the coronavirus vaccine, according to the latest official figures. Experts have warned Britain is "still not out of the woods" amid concerns over new variants and the risks of the public breaching restriction rules. /IANS