Washington's health chief expressed scepticism about Russia's claim of developing the world's first safe coronavirus vaccine, pointing to the lack of data from its initial trials, according to AFP.

Moscow said its vaccine offered “sustainable immunity” against the virus, but Western scientists have previously raised concerns about the development speed of Russian treatments, suggesting researchers were cutting corners.

US Health Secretary Alex Azar echoed those concerns as he wrapped up a three-day visit to Taiwan.

“It's important that we provide safe, effective vaccines and that the data be transparent [...] This is not a race to be first,” he told reporters during a conference call.