Words by ITV News Multimedia Producer Suzanne Elliott
A total of 1.4 million people in private households are estimated to have had the virus last week, up 43% from 989,800 the previous week.
This is the highest estimate for total infections since the start of May, but is still well below the record high of 4.9 million which was reached at the end of March.
BA.4 and BA.5 were behind a recent wave in South Africa, and are gaining ground across the United States.
BA.5 is believed to be driving a surge in cases and an uptick in hospitalisations in well-vaccinated Portugal.
With Covid restrictions lifted in many countries, and holidays - long queues and cancelled flights aside - back on, could these latest subtypes fuel another spike in Covid cases, and another wave in the UK?
What are BA.4 and BA.5?
The BA.4 and BA.5 are sub-variants of Omicron which emerged at the close of 2021. They are the latest variants of Covid-19 that is, like all viruses, continuing to adapt to an increasingly immune population.
BA.4 and BA.5 share many of the same mutations as the original Omicron variant, but have more in common with the BA.2 variant, previously referred to as "stealth Omicron".
But there are notable differences, specifically that their spike proteins - the part of the virus that attaches to receptors on human cells - are different.
Where have Omicron BA.4 and BA.5 cases been found?
BA.4 and BA.5 were first detected in South Africa in January and February 2022, respectively, and since then have become the country's dominant variant. According to the World Health Organization (WHO), South Africa is now coming out the other side of its latest wave.
Portugal, a popular holiday destination for British visitors, now has the world's second-highest Covid infection rate, driven, experts believe, by BA.5. More worryingly, death rates and hospitalisations are also on the rise.
Germany is also seeing cases and the country is preparing for a Covid surge in the autumn.
Are we seeing BA.4 and BA.5 sub-variant cases in the UK?
Omicron BA.4 and BA.5 were identified as variants of concern in the UK in May and appear to be gaining ground. Both BA.4 and BA.5 are already on our shores.
Indeed, Friday's ONS UK Covid infection figures revealed a slight rise in cases for the first time in two months, an uptick scientists believe is being driven by these new variants.
Sarah Crofts, Head of Analytical Outputs for the Covid-19 Infection Survey, said: “Today’s data shows a mixed picture for infection rates across the UK, with small increases in England and Northern Ireland, likely driven by increasing trends in Omicron BA.4 and BA.5 variants.
“Infections with Omicron BA.2 remain the most common variant of Covid-19 and continue to decrease across much of the UK. We will continue to monitor the data closely.”
Paul Hunter, Professor in Medicine at the Norwich School of Medicine told ITV News, BA.2 infections have been falling since about early April, but cases of BA.4 and BA.5 have been increasing "quite quickly".
"My guess is, that it was about three days ago they became more than 50% [of cases]. So what we'll see is that over the next few days, the rate of increase in total cases will get greater, until we get to the point where BA.4 and 5 are by far the dominant, and it will probably take another week or two before we get the most rapid increase," he said.
Will we see a new Covid wave?
"It's certainly looking like that," Prof Hunter, told ITV News, but how big the wave will be is unknown. The BA.4 and 5 wave that hit South Africa did not show a rise in hospitalisations.
"How big a wave given that many people - the large majority of people in this country - have actually had Covid already and many people have had Covid more than once... If we follow what's happened in South Africa, that wave will be relatively small compared to the big Omicron waves - the two big waves of Omicron we've had in the last six months," Prof Hunter said.
"I think the best guess is that, yes, we will see infections rise but they won't be translated that much into severe disease and deaths," he said.
But Prof Hunter cautioned: "South Africa is not quite the same as the UK; they've had less vaccination and many more infections than we've had. So they may be actually better may have been actually better protected because of multiple repeated infections in the past."
Independent SAGE, a group of scientists providing advice during the Covid pandemic, suggested a new wave "might be on its way in a month or two".
But while it was once easy to see what was coming by looking at trends in other countries, with different vaccination and immunity rates across borders, it is getting harder to predict just how much of an impact a new variant-fuelled wave could have.Are these variants more transmissible?
The UK Health Security Agency found both new variants were likely to have a “growth advantage” over BA.2.
Will vaccines and infection work against these variants?
The current vaccines were all designed to work against the original Wuhan variant and with each mutating turn the virus takes, the more vaccine escape there is likely to be.
Initial findings suggest BA.4 and BA.5 have a degree of “immune escape” – meaning the immune system can no longer recognise or fight a virus – which is likely to contribute to their growth advantage over BA.2, the UKHSA have said.
According to Dr Wesley Long, a pathologist at Houston Methodist in Texas, lab data suggests a prior infection with the original Omicron is not very protective against reinfection with the new mutants.
A study released before it was reviewed by other scientists, by researchers at Ohio State University, found that Covid patients in intensive care with Delta infections induced antibodies that were better at neutralising the new mutants than patients who caught the original Omicron.
Will the UK's dramatic Omicron wave protect us?
WHO said it is tracking all Omicron sub-variants as “variants of concern," and found countries which had a significant Covid wave fuelled by Omicron sub-variants BA.2 appeared to be less affected by other sub-variants like BA.4 and BA.5.
Salim Abdool Karim, an infectious diseases expert at the University of KwaZulu-Natal, said it appeared that South Africa had passed its most recent wave of Covid-19 caused by the BA.4 and BA.5 sub-variants; the country has been on the forefront of the pandemic since first detecting the Omicron variant last November.
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