Campaigners for clinically extremely vulnerable people have called for urgent government action to ensure they receive Covid booster vaccinations as soon as possible, after members of the government’s vaccines watchdog cast doubt on plans for them to begin early next month. The Joint Committee on Vaccination and Immunisation (JCVI), which advises ministers, met on Thursday morning and some members believe that significantly more work is needed before booster jabs can be rolled out. The concerns centre on the clinical benefits of booster vaccinations, with trials due to continue until late this month, and any wider risks to vaccine confidence. Officials say other JCVI members still believe early September is a realistic target. The date is not a formal timetable, but the Department of Health and Social Care and the NHS have talked about it as an intended starting point. Speaking on a trip to Cumbria, the health secretary, Sajid Javid, said he was confident the scheme would begin, but said only that this would be “some time in September”. On Thursday, confirmed daily UK Covid cases stood at 36,572 amid a general upward trend this week. Blood Cancer UK said there was particular worry at rising cases among people with the condition. Vaccines can offer less protection to these patients but trial results are due soon on whether a booster jab could help. Helen Rowntree, the head of research at the charity, said: “If this research shows a third dose does improve immune responses in people with blood cancer, it is vital that the government then rolls out booster jabs to this group with urgency.” Sal Brinton, a Lib Dem peer who has campaigned over Covid issues for people with extreme clinical vulnerabilities, said current government advice for the 3.5 million-plus people in this category was “shielding by any other name”. She said: “What do they propose for this group? Or do we just sit at home? The problem is that outside is now more dangerous for those with reduced or zero antibodies as many people are not using masks or socially distancing.” One JCVI source said the issue was complex, pointing to one Oxford University study indicating that if people were given a “mix and match” combination of vaccines for their first and second jabs, the side-effects could be worse, with potential implications for the idea of using a different jab for a booster “The jury is still very much out on what happens,” the source said. “One of the consistent things we have found is that when we undertake clinical trials, the results can be surprising.” Another JCVI source said that while the focus remained on people who were clinically very vulnerable, a worry was the potential impact of pushing booster vaccinations on a public within which the take-up of other jabs, for example for children and teenagers, had “dropped off a cliff” since the start of the pandemic. “The confidence in the Covid vaccines has been fantastic, but confidence is very fragile and we don’t want to harm it,” they said. “There is evidence that if someone has a reaction to a vaccine it can put them off having all vaccinations in the future. The most important message right now is to stress that anyone who has not had their first or second vaccination should do so.” Other issues discussed at the meeting include the regulatory, legal and logistical hurdles of a third vaccination. It is understood some JCVI members are also concerned about the UK using large numbers of vaccine doses for booster injections of limited clinical value when they could be sent overseas, but the consideration is not part of the committee’s remit. A government spokesperson said: “We are preparing for a booster programme to ensure those most vulnerable to Covid-19 have protection extended ahead of winter and against new variants. “Any booster programme will be based on the final advice of the independent Joint Committee on Vaccination and Immunisation. Until we receive the independent JCVI advice no decisions can be made on wider requirements for those who receive booster jabs.”