NHS and social care staff will be given antibody tests revealing whether they have had coronavirus from next week, ministers are to announce on Thursday. In a move designed to reduce frontline workers’ anxiety and provide data on how many people have had Covid-19, hundreds of thousands of workers will be offered access to the blood tests, which must be processed in laboratories. However, experts warned of the risk of creating a false sense of security for those with positive antibody test results, as they offer no guarantee of immunity. While it is hoped that the presence of antibodies reduces or removes the risk of reinfection, this has not yet been proved. The length of any immunity gained is also unknown. Dr Claudia Paoloni, president of the Hospital Consultants and Specialists Association, said: “The ability to assess who has and has not already had this virus is a major milestone, but there are still a number of unknown factors. “As we learn more about the role of antibodies, this could open the door to different ways of working and reduce the level of risk to NHS staff by allocating those who have had the virus to care for Covid-19 patients. But we must be clear that huge uncertainties remain while we do not know the level and length of any immunity which antibodies will offer. “The new test’s arrival should not simply be seen as a green light to reduce PPE and other protections for NHS staff who test positive.” Either Boris Johnson or Matt Hancock, the health secretary, is expected to make the announcement on Thursday, the Guardian understands. Public Health England (PHE) validated two laboratory-based antibody tests from Swiss-based Roche and US-based Abbott last week, and another – from the Welsh firm Ortho Clinical Diagnostics – this week. Initially, priority will be given to frontline hospital personnel working most closely with Covid patients, such as intensive care staff, those working on coronavirus wards and doctors and nurses in A&E units. Scientists will monitor those who test positive to see whether their antibody levels drop over time and whether any of them fall ill again. Despite the lack of guaranteed immunity, one source with knowledge of the plan expressed hope that the tests would instil confidence in NHS workers. “The intention is that NHS and care staff will get these tests in the first instance to see if they’ve had the virus, so that they can feel able to go back to work safely, knowing that they will have at least some immunity,” the source said. A senior figure in the NHS added: “Antibody tests for staff could be a real game-changer in letting hospitals restart services. However, they won’t be able to tell us for months if people who have had the virus are immune.” Meanwhile, a private testing bonanza looks set to take off, with private GP clinics and the high street chemist Superdrug offering antibody tests supplied by Abbott for sale to the public. Ortho Clinical Diagnostics’ newly PHE-approved test outperformed the other two. Ortho, based in Cardiff for 40 years, says its test is 100% specific for Covid-19, which means it does not confuse the antibodies produced in response to the virus with those from other coronaviruses, including the common cold. Roche’s test has been validated by PHE as 99.8% specific and Abbott’s as 99.6% specific. The Abbott tests sold by Superdrug for £69 and private clinics such as Babylon and the Independent General Practice in Wales are “home” tests in that people can take a blood sample at home after buying the kit, but they must post it to a lab for processing. Rapid fingerprick tests that give an instant result, like a pregnancy test, have not yet proved accurate enough for approval. The accuracy of the Superdrug test is given on their website as 97.5% because people will have to lance their finger to obtain blood themselves rather than have a health professional do it, which adds the risk of error. Scientists emphasised warnings over the risks of antibody tests for the public. “If a person takes a test and gets a false positive, they may assume they have been exposed and that they have immunity when they do not,” said Adam Finn, professor of paediatrics at the University of Bristol. “So the bottom line is: don’t spend money and time on any test unless you have a very clear idea of what the result does or does not mean for you and what you are going to do or not do if you get a positive or negative result.” Dr Simon Clarke, associate professor in cellular microbiology at the University of Reading, said the tests were “good for satisfying people’s curiosity, but no more”. “Having these antibodies is a reliable way of confirming that someone has been infected previously. Their presence does not indicate that someone is immune, and it should be remembered that any post-infection immunity may dwindle rapidly … We just don’t know enough about what it takes to make someone immune to Covid-19 to accurately test people,” he said. Ortho Clinical Diagnostics has two lab-based tests. PHE has validated the first of these, which detects a single antibody called IGG, and is expected to validate the other, which detects all antibodies produced, this week. Paul Hackworth, its UK managing director, said both were 100% specific for Covid-19. “We are the only one of the major companies [producing antibody tests] with UK manufacturing,” he said. “That helps with the supply chain.” Their machines are already common in hospital labs, he said, and are easier than some to run because they do not require a water supply, but just plug into an electric socket. The machines can run 150 tests an hour. There were various uses for the test, he said. “The sense we get is that initially it will be used in returning staff and to serve the needs of the vaccine,” he said. It will be important to find out how quickly antibody levels that are raised after vaccination wane over time. The other major use of antibody tests is across populations, to find out what proportion of people have been infected. They can help decide whether some groups of people are more likely to get infected than others and whether there are regional variations. Several studies have already begun, including one from Biobank, which is planning to test 20,000 participants, their children and grandchildren. Stephen Powis, NHS England’s national medical director, confirmed at the Downing Street briefing that antibody tests would be given first to NHS and care home patients and staff. “They will be rolled out through health and social care settings. Their use will be in those settings and surveillance so we get some impression of how many people in this population have been infected by the virus,” he said. He cautioned against the use of tests available to the public for use at home. “The antibody test shows you that you have had the virus. What we don’t absolutely know at the moment is whether having antibodies means that you won’t get the virus again,” he said. Scientists would know that over time by following those people who had antibodies to see whether they get reinfected.”