Boris Johnson’s top scientific advisers warned on Tuesday that the UK will see a surge in coronavirus cases later this year even if most of the population is vaccinated.

Prof Chris Whitty, chief medical officer for England, also said that “things can quickly get bad” and “a lot more people will die” if restrictions are eased too quickly.

He said there was minimal scope to speed up the UK’s roadmap out of lockdown, with five weeks required between each step to analyze the effect of lifting restrictions on case numbers.

Most Covid-19 measures are due to be dropped by June 21 but some MPs are pushing for that date to be brought forward due to the success of the UK’s vaccination program.

More than 22.3 million people have received a first dose of a Covid-19 vaccine in the UK, according to government figures.

But Prof Whitty said vaccines are “not 100 percent effective” and some people will not be inoculated against Covid-19.

He said young people in particular would remain major spreaders of the virus.

“At some point we will get a surge in the virus,” he said, adding that the disease will find a way to spread to unvaccinated people.

“It may happen later in the summer if we open up gradually, or there is the seasonal effect and it might happen over the autumn and winter.”

He said the UK was taking “big blocks of risk” with the current easing measures, advising MPs against speeding up the program.

In a further warning, Prof Whitty said moves to tighten measures in Europe following another surge demonstrated why “this is not all over”.

“I think it’s very easy to forget quite how quickly things can turn bad if you don’t keep a very close eye on it,” he said.

“If you start shunting things forward you will get these higher peaks.”

Just as the flu virus changes every year – so I would expect this virus to change over time. I do not think zero-Covid is possible … nothing suggests this virus is going to go away soon.”