Coronavirus case rates are "still very high", England's chief medical officer has warned.
Professor Chris Whitty also said COVID-19 cases are "rising again", as the UK recorded its highest ever daily tally on Monday.
A total of 226,525 cases were reported, according to the latest government data, although this also included figures for Saturday and Sunday, as well as reinfections, which have been part of daily tallies since 31 January.
That figure was more than 50,000 higher than the 170,985 cases reported the previous Monday, which also included weekend infections.
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A total of 607,736 people have tested positive in the seven days up to 21 March, an increase of 37% - or 163,536 people - from the previous weekly period.
On Monday, Prof Whitty tweeted: "COVID-19 rates are still very high, and rising again.
"Vaccines substantially reduce rates of severe disease and hospitalisation but there is some reduction of effect over time.
"If you are over 75 or immunosuppressed and the NHS contacts you for a booster please take up the offer."
A spring COVID-19 booster jab became available to those aged 75 and over, as well as those in vulnerable groups, on Monday.
The NHS said more than 600,000 people will be contacted this week and invited to book their booster, which will eventually be made available to about five million people.
On Monday, Scotland recorded its highest ever daily number of patients in hospital with coronavirus.
The figures showed 2,128 patients were in hospital with COVID-19 on Sunday, with 31 of those in intensive care.
Health secretary Sajid Javid said on Monday there were 11,500 people with coronavirus in England's hospitals, but that nearly 60% of them were being treated for something other than COVID-19.
According to figures published by the NHS on Monday, the number of people in hospital with COVID-19 in two regions of England has climbed to the highest level for more than a year.
South East England has now joined the South West in recording patient levels last seen in February 2021, surpassing the peaks reached in the previous surge of infections at the start of 2022.
A total of 1,956 people with COVID-19 were in hospital in the South East on Monday, the highest since 19 February last year.
And in the south west, 1,365 patients were recorded on Monday, the highest level since 9 February 2021.
In both regions about half of patients in hospital with COVID-19 are being treated primarily for something else.
Figures published on Friday by the Office for National Statistics (ONS) showed that infection levels are continuing to rise across most of the UK, with 3.3 million people estimated to have coronavirus in the week to 12 March, up from 2.6 million the previous week.
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