Scientists had warned us not to take Omicron too lightly until infections had spread into the vulnerable age groups
Scientists had previously warned about the risk of increased inter-generational mixing over the festive period.
With younger people bearing the worst of the new variant’s spread until then, it was feared more mixing would lead to a rise in infections among vulnerable groups most at risk of severe illness.
Cases among people aged 80 and over were 169% higher in the week to 6 January than they had been in the week to Christmas Day – the biggest increase of any age group.
And hospital admissions and deaths have risen too – particularly among at-risk age groups.
Here’s everything you need to know.
What happened to infections before and after Christmas?
Our interactive heat map, created using data from the UK Covid dashboard, reveals how Covid cases began to spike among younger groups initially in England.
At the start of December, the number of positive cases per 100,000 people was by far the highest among children aged 10 to 14, followed by five to nine year olds.
Midway through the month, the darker bars show how Covid cases rose among young and middle-aged adults, but remained relatively low among people aged 60 and over. The NHS says people aged over 60 are at higher risk, with the risk growing with age.
But as Christmas came and went, the high infection rate began to bleed out into the older age groups.
As of the week ending 6 January, infections were still highest among people aged 25 to 29, at 2,869 cases per 100,000 people.
But infections among the older age groups are much higher than they were before Christmas.
In the week to 6 January, there were 20,157 cases detected among people aged 80 or over, a rate of 705.9 per 100,000.
That was a 169% increase on the week ending 25 December, when there were 7,498 cases, or 262.6 per 100,000. It is also the highest it has been at any point in the pandemic.
You can find out which areas of England now have the highest infection levels among people aged 80 and over here.
Have the experts been proved right?
After Omicron cases surged in the UK, scientists spent weeks warning that it should not necessarily be assumed to be mild just because hospital admission and death figures remained low.
This is partly because there is always a lag between when somebody becomes infected and the point they become sick enough to need hospitalisation, and another lag between that and death.
But it was also because the new variant had spread most quickly among younger age groups first, who have always been at a lower risk of becoming seriously ill from Covid.
Only when the virus passed into older, more at-risk people would the true picture begin to emerge.
In South Africa, where much of the early data on Omicron came from, the population is relatively young – much more so than the UK, with a lower average age.
How many older people are in hospital now?
In the week to 9 January, 2,513 people aged 85 and over were admitted to hospital with Covid, a rate of 178.7 admissions per 100,000 people. That has come down slightly from a peak of 180.5 admissions in the week to 5 January but was still a week-on-week increase.
The average across all age groups was 24.9 admissions for every 100,000 people.
Admissions among this age group rose sharply from around 18 December, with a rapid and sustained rise until early January.
The rise among people aged 85+ was more steep than among almost any other age group after 21 December and into January.
The rate of increase was surpassed at times by that for children aged 0 to five, however, for whom admissions rose to the highest level recorded in the pandemic to date.
How many people are dying?
The number of deaths in England also began to rise in the last week in December – and is still increasing.
In the week to 6 January, 510 people aged 80 and over died within 28 days of a positive Covid test.
That was up by 26.1% on the previous week when there were 424. There has been a sustained period of increase in weekly deaths in this age group since 21 December, with a slight dip from 5 to 6 January.
While deaths had originally risen fastest among the 80 and over and 60 to 69 age groups, deaths across people under 60 have also now seen a jump.
In the week to 6 January, deaths among people aged 0 to 59 rose by 26.9%, from 93 to 118.
A message from the editor:
Thank you for reading. NationalWorld is a new national news brand, produced by a team of journalists, editors, video producers and designers who live and work across the UK. Find out more about who’s who in the team, and our editorial values. We want to start a community among our readers, so please follow us on Facebook, Twitter and Instagram, and keep the conversation going. You can also sign up to our newsletters and get a curated selection of our best reads to your inbox every day.