Numerous studies have found that people who recover from Covid-19 rarely become reinfected in the months that follow, according to a November paper in the journal The Lancet Infectious Diseases. And yet the US and Germany are among the countries with a more narrow view of how long immunity from a previous infection can be recognized before a vaccine is required, namely 90 days. EU states have agreed that travellers should be able to move freely within the union from February 1 without further requirements if they present valid proof of recovery in the past 180 days – six months. However EU cou…