Covid 19 coronavirus: Virus variants likely evolved inside people with weak immune systems 17 Mar, 2021 01:28 AM 5 minutes to read Nurses and doctors tend to a patient in a Covid-19 Intensive Care Unit at the Curry Cabral hospital in Lisbon. Photo / AP New York Times By: Apoorva Mandavilli Growing evidence suggests that people with cancer and other conditions that challenge their immune systems may be incubators of mutant viruses. The version of the coronavirus that surfaced in Britain late last year was shocking for many reasons. It came just as vaccines had offered a glimpse of the end of the pandemic, threatening to dash those hopes. It was far more contagious than earlier variants, leading to a swift increase in hospitalisations. And perhaps most surprising to scientists: It had amassed a large constellation of mutations seemingly overnight.