The UK will go through the “most dangerous time” of the pandemic in the weeks before vaccine rollout has an impact.
Prof Chris Whitty urged people to minimise all unnecessary contact with others.
The next few weeks will be “the worst” of the pandemic for the NHS, he said.
Thousands more people are due to receive a vaccine this week after seven mass centres opened across England.
NHS England said hundreds more GP-led and hospital services would also open later this week.
But with all centres, people will need to wait until they receive an invitation.
The government is aiming to offer vaccinations to around 15 million people in the UK – the over-70s, older care home residents and staff, frontline healthcare workers and the clinically extremely vulnerable – by mid-February.
