A study of COVID-19 patients has found that they lost protective immunity within two to three months of recovery. Experts say that raises questions about social distancing, immunity passports and vaccines. By the time people recover from a viral infection, they have usually had an immune response and developed protection against the disease. That is, the immune system has produced antibodies that will recognize the virus if it attacks a second time, and those antibodies will know how to fight it off. But a recent investigation at Schwabing Hospital in Munich, Germany, suggests this might not be the case for SARS-CoV-2, the coronavirus that causes the disease COVID-19. Clemens Wendtner, a chief physician at the hospital, tested COVID-19 patients for immunity after they had been treated for the disease at the end of January 2020. The tests showed a significant decrease in the number of antibodies. Wendtner says “neutralizing” antibodies, which stop a viral attack, fell in four out of nine of the patients who were tested, within two to three months. Those findings coincide with a similar investigation done in China. That study also found that antibodies in COVID-19 patients do not persist in the blood. Further research is still required. But these initial findings suggest that a second infection is possible, where normally patients would have developed an immunity. And that may change the way experts handle things like the easing of social distancing measures. Antibody testing is crucial to determining the “immunity status” of a community Our bodies develop immunity to the virus by producing antibodies. marrow, where they produce antibodies against infections we have had. Those plasma cells can persist for years — keeping us immune for years. If, however, SARS-CoV-2 antibodies do not last in blood, as those recent studies suggest, recovered patients have little protection and can be re-infected. Which would bring us back to square one, where everyone is at risk of infection. One way to stop a virus spreading in a population is by developing “herd immunity.” That’s when enough people have been infected, recovered and developed a lasting immunity. But now that secondary infections with SARS-CoV-2 seem possible, experts are questioning the easing of social distancing measures, or whether it’s a good idea to issue recovered patients with so-called “immunity passports,” allowing them to roam freely. Scientists still don’t know why those antibody levels decrease over time. To compare: Antibodies against other types of coronavirus last in the blood for at least one year. That’s true for SARS-CoV, the virus that caused a 2003 outbreak in Southeast Asia, and MERS-CoV, the virus that caused a 2012 outbreak in the Middle East. All this has implications for the development of a vaccine against SARS-CoV-2. There are at least 130 candidate vaccines in clinical or pre-clinical trials worldwide. Conventional vaccines use weak or inactive versions of a virus to produce an immune response and protective antibodies. Newer types, known as DNA or RNA vaccines, hope to use genetic information from the virus to achieve the same result. But if natural antibodies decrease so quickly, how long will antibodies that are produced as a response to a vaccine last? As vaccines for SARS-CoV-2 have yet to be approved, we have a way to go before we find out.