Pressures on intensive care units are seeing one in 10 patients transferred to a different site.
Boris Johnson said he looked forward to "deepening the longstanding alliance" between the UK and US.
The vaccination centres are temporarily closing in south Wales after ice and snow were forecast.
Booking a jab by following a link in an email meant "depriving someone else" of a vaccine, he said.
One says he is surprised Boris Johnson shared the early data when it is "not particularly strong".