One of the most concerning issues since the emergence of the Covid-19 virus has been whether those who have had it can get it a second time – and what that means for immunity. On Monday, both Sir Patrick Vallance, the government’s chief scientific adviser, and Prof Chris Whitty, Boris Johnson’s chief medical adviser, sought to reassure the public. Those who have had the virus once will develop some immunity, they said – and it is rare to get an infectious disease again. When Vallance was asked on Monday if the Japanese case meant herd immunity was no longer achievable, he replied that some people do catch infectious diseases a second time, but that it is a rare occurrence. There was no evidence to suggest that it would occur with the coronavirus, he added. As coronavirus closes schools, teachers and families brace for massive experiment in online education As of Monday afternoon, 35 states, including Washington, had mandated school closures in an effort to slow the spread of the virus; at least 35.9 million children are now displaced from their classrooms, according to a tally by Education Week. As school leaders look for ways to minimize the disruption to children's learning — and try to avoid extending the school year through the summer — teachers at thousands of schools all across the country are scrambling for ways to teach children who are holed up at home. In many of the states where governors mandated school closures, the order went into effect immediately or with just a day's notice — not even enough time to learn how many students have access to technology at home.