COVID-19: Is the UK on the brink of a new wave – and is 'immune imprinting' to blame?
Scientists tell Sky News that it is getting harder to predict how the UK will fare with different COVID variants because of 'immune imprinting', which means everyone's immune system reacts to them differently depending on their specific infection and vaccine history.
New COVID data suggests that after months of declining case rates, the number of people testing positive across the UK is starting to go up again.
For the week ending 2 June, the Office for National Statistics (ONS) said there were "early signs of a possible increase in percentage of people testing positive for coronavirus".
It was most noticeable in England and Northern Ireland, where the positivity rate is one in every 70 people and one in every 65 people respectively.
And it is being driven by new sub-variants of
Omicron - BA.4 and BA.5.
A separate Imperial College study released on Tuesday suggests that being infected with Omicron
does not provide much immune protection from being reinfected.
So with infection rates on the rise and more chance of reinfection - should we be worried?
Why are cases going up again?
With COVID tests no longer free and widely available, experts now rely on people's responses to the ONS weekly infection survey to see whether cases are going up or down.
After months of steep decreases, the ONS data shows positivity rates flattening at the end of May in each of the four nations, although it says trends for Scotland and Wales are "uncertain".
But since then, there has been an uptick, largely driven by Omicron's two new sub-variants - designated variants of concern (VOC) by the UK Health and Security Agency (UKHSA) on 20 May.
Dr Stephen Griffin, a virologist at the University of Leeds, tells Sky News: "Although overall infection levels have been coming down, if you look at the variant split, BA.4 and BA.5 in particular are becoming more dominant.
"There are some interesting changes with those two because they have increased antibody-evasive properties."
The Imperial study published this week was carried out on 700 London health workers from March 2020 onwards.
Although they all had three vaccine doses, their Omicron reinfection rates differed.
That is because, they say, people's protection against new COVID variants depends on their specific vaccination and infection history - a concept called immune imprinting or 'original antigenic sin'.
Dr Peter English, former Public Health England consultant in communicable disease control, says: "There was a big concern in the beginning with vaccines and original antigenic sin.
"It's whereby if you are infected with an earlier variant and produce an immune response to it, when you're infected with a new variant, your body essentially produces the original immune response, which is the wrong one, because it doesn't realise it's a new variant, which needs a different immune response.
"We're beginning to see signs that this is the case with these new Omicron sub-variants.
"So we might have been unduly hopeful it wouldn't be."
Dr Griffin adds: "The reason these variants are spreading still is because the pool of people they can infect is growing - because people who have already been infected can be infected again."
Can we call it a 'new wave'?
The UK's first Omicron wave came in December, soon after South Africa's, followed by a second driven by sub-variant BA.2 in around March.
BA.2 still makes up most UK infections, and while BA.3 largely remained in South Africa, the emergence of BA.4 and BA.5 in May is effectively another wave, Dr Griffin says.
But he adds: "It's difficult to predict how big this wave might be."
South Africa has already had a BA.4/5 wave, with cases already flattening. But it has been completely different to the one experienced in Portugal - where death rates were much higher.
"This speaks to the idea that as time goes on it's going to get more and more difficult to predict how countries will fare with one variant or another," he says.
"That's because we have a different pattern of immunity - we're in a new era now where that is really important."
So comparing how BA.4 and BA.5 have affected other countries, does not appear to be useful.
Should we be worried?
While the majority of Britons have returned to normal life, cases going up again will have consequences, Dr English warns.
"Some people remain very anxious, but there are many others who have decided they can't cope with COVID being a thing anymore so they're going to pretend it doesn't exist. And that will mean more risk for all of us."
The virus being more prevalent again will force the clinically vulnerable back into their homes and could see more people with Long COVID or more serious symptoms of it, he adds.
Vaccination rates and immunity from vaccines have also waned and with masks and isolation no longer mandatory, it is likely to spread quicker than before.
Both scientists predict that as in previous years, cases will increase in the winter with more time spent indoors.
But Dr English adds: "We shouldn't be complacent, rates are going up quite quickly here - and in the US.
"People will come back from their summer holidays and schools will become a driver for transmission as they have done before.
"But I think we should be a bit worried - even now."
"Prevalence of this virus matters," Dr Griffin says. "We're about to see the number of Omicron deaths overtake Delta - even though it is less likely to cause severe disease.
"At the moment there's no public health safety net that says 'this will happen if we don't do this, so here's what we can do to stop that'.
"And it's that safety net, not lockdowns, but those sensible measures, that would allow all parts of society to live with this virus."
