http://www.sciencemag.org/news/2021/01/will-delaying-second-doses-covid-19-vaccines-spur-viral-resistance

Visitors line up to receive an injection of a COVID-19 vaccine at a National Health Service center in Birmingham, U.K. Because of scarce vaccine, the United Kingdom has stretched the interval between doses. 

Science’s COVID-19 reporting is supported by the Pulitzer Center and the Heising-Simons Foundation.