A coronavirus variant which escapes vaccine immunity could take the world by surprise, Sir Patrick Vallance has warned.
Speaking at a virtual Royal Society conference, the Government's chief scientific adviser for England also said the "world needs to be ready" for inevitable future pandemics which look very different to the current one.
Sir Patrick told scientists at the meeting about the 100 Days Mission, an initiative which aims to "prevent future pandemics before they start", according to the Government.
The mission works towards a target of being able to develop effective vaccines, therapeutics and testing within 100 days of an epidemic or pandemic threat being identified.
Sir Patrick told the Royal Society meeting: "It's very obvious to everyone in this meeting that there will be a future pandemic.
"That I think is clear.
"It's also clear this one is not over and we've got very high infection rates at the moment.
"And the room for this virus to evolve remains very large, so we could be taken by surprise again with a variant that escapes immunity."
He added: "We've got no idea what the next pandemic might be and it certainly won't be the same as this one.
"Whatever it is, the world needs to be ready to respond."
Sir Patrick also said he is "pleased" that "a big uplift" of £5 billion in funding up to 2025 for life sciences research, including work aiming to prevent future pandemics, was included in the Spending Review.
But he added that a decade of "underfunding" for Public Health England (PHE) undermined the UK's response to the pandemic in 2020.
He said: "Some things were underfunded, and that underfunding undermined the ability operationally to do things.
"The underfunding of Public Health England for virtually a decade beforehand was an important part of why certain things were difficult and it's very important that we don't fall into that trap again."
Sir Patrick's speech comes as free coronavirus testing comes to an end this week for most people, as part of the Government's Living with Covid plan.
From Friday, most people will need to shop on the high street for paid-for tests if they want them.