International travel should reopen slowly, with any traffic light system having the potential to be “leaky” to Covid variants, a senior scientist has said. Professor Robin Shattock, head of mucosal infection and immunity at Imperial College London’s department of medicine, said an ideal scenario would be for people to quarantine when they return from any country – though this was unlikely to be seen as a practical option. In a wide-ranging interview, he said it was possible coronavirus will become “much more of a fairly trivial infection” for most people, while it was still uncertain whether the entire population would need to be vaccinated again each winter.