Summer holidays overseas will depend on European countries catching up with the UK on their vaccination programmes, Professor Jonathan Van Tam has said.
England's Deputy Chief Medical Officer said many European countries are behind us on vaccine rollout - and the possibility of overseas travel will depend on what other countries will "say and do".
He told a No 10 news briefing: "We are still in a zone of great uncertainty about what the virus will do next.
"On top of that, many of the vaccination programmes in Europe - which is a place where we frequently go on holiday abroad - are running behind ours.
"Clearly, whether we can go on holiday abroad to places such as Europe depends on what other countries will say and do in terms of foreign tourism.
"There has to be great uncertainty at the moment."
Encouraging people to continue to come forward for their first and second doses, Professor Van Tam added: "We have to be patient. We have to push on with the vaccine programme."
Government data up to February 28 shows that of the 21,091,267 jabs given in the UK so far, 20,275,451 were first doses - a rise of 185,900 on the previous day.
A further 104 people died within 28 days of testing positive for Covid-19 as of Monday - the lowest daily figure since October 26 - while there were another 5,455 lab-confirmed cases in the UK.
Meanwhile, Matt Hancock defended the Government's border arrangements following the detection of the cases of the worrying Manaus variant.
The Health Secretary said home quarantine measures were already in place and travel restrictions on Brazil had been imposed before the hotel policy was implemented.
Mr Hancock said: "All the evidence is that the five cases that we know about followed those quarantine rules and that, I hope, is very reassuring to people.
"There is no evidence that the sixth case did not follow those quarantine rules - we need to obviously get in contact with the person in question."
The test was taken on February 12 or 13 and "we haven't seen any further knock-on transmissions in the data".
Public Health England (PHE) has identified six UK cases of the concerning P1 variant first detected in the Brazilian city of Manaus - three in England and three in Scotland.
Three cases are Scottish residents who flew to Aberdeen from Brazil via Paris and London, who all tested positive while self-isolating.
Other passengers who were on the same flight to Aberdeen are now being traced.
The other two cases in England are from the same household in South Gloucestershire after one person returned from Brazil on February 10 - just days before the Government's hotel quarantine rule came into force.
Two other people in the same household have also tested positive but are not currently included in the UK case total of six, while tests on their type of coronavirus continue.
Officials are searching for passengers who were on the Swiss Air flight LX318 from Sao Paulo to Heathrow, via Zurich, which landed on February 10.
Dr Susan Hopkins, of PHE, said they were tracking "very closely" the new Brazilian P1 coronavirus variant following the discovery of six cases in the UK.
She told the press conference: "The current vaccines have not yet been studied against this variant and we will need to await further clinical and trial data to understand the vaccineeffectiveness against this variant."
Dr Hopkins said they were in the process of trying to track down the one person who has yet to be identified who is believed to have taken a test on February 12 or 13.
