Sir Patrick Vallance has warned the next Covid variant could be worse than Omicron as the virus continues to evolve.
The Government's Chief Scientific Adviser said it is "a mistake" to believe the more Covid evolves, the less serious its mutations will become.
The Omicron variant spread rapidly across the UK in the run-up to Christmas when the R number was estimated to be around 1.3 which meant on average every 10 people infected 13 people.
Sir Patrick said Covid cases may have peaked but there will be more hospitalisations and deaths from this current wave.
Experts believe the vaccines have helped keep the most severe cases at bay. But he told MPs it was not a "credible" strategy to give people booster jabs every four months.
"This virus is not going away. It hasn’t stopped evolving. It’s been quite an unstable period but the virus is changing very rapidly," Sir Patrick said.
"It’s a mistake to assume all evolution will drive to reduce severity," he added.
Hospital cases are also rising because of this variant, but the vaccines are helping to keep severe cases at bay, experts have said.
As of March 30th there have been 19,000 Covid hospitalisations.
Sir Professor Chris Whitty said last week the NHS is coming under "significant" pressure across England and he expects hospitalisations to continue increasing until April.
It comes as free Covid tests are set to end on Friday in England.
When asked if he was concerned by the sharp rise of Covid cases recently, he told MPs: "We've got very high levels of infection at the moment, as indeed many other countries.
"It is very important that actually, at the moment the realised severity, because of vaccines and other things, is being kept under control."
Figures published by the ONS last Friday showed the total number of people likely to have coronavirus in the UK has risen from 2.4 million in the week to February 26 to 4.3 million in the week to March 19.
The latest wave of infections is being driven by the Omicron variant BA.2, a more transmissable form of the virus, the ONS said.
