Tim Spector, an epidemiologist at King's College London, previously told Insider that while there's no evidence that Delta is deadlier, it is more infectious, and "because of that extra stickiness, it's going to still keep breaking through the vaccine group." More than half of Scotland is fully vaccinated, and 71% of Scots have received at least one dose of a vaccine. But the country is suffering its worst wave of infections. "You cannot explain the explosive epidemic in Scotland, in a pretty highly vaccinated population, if they're not playing a role in transmission," Murray said of vaccinated people... Murray says COVID-19 outbreaks are being investigated in US groups "that are 90%-plus vaccinated." "That could only be occurring if they're transmitting amongst each other," he said. "There's no doubt in my mind."