COVID cases in the UK are rising rapidly once again, driven by the spread of the new BA.4 and BA.5 Omicron sub-variants.
Some 2.7 million people are estimated to have had COVID last week, a rise of 18% on the previous seven days, according to the latest figures from the Office for National Statistics (ONS).
The ONS figures show 1 in 25 people in England and Northern Ireland had COVID in this timeframe, compared to 1 in 20 in Wales and 1 in 17 in Scotland.
While numbers are some way below the record high of 4.9 million weekly infections seen at the peak of the Omicron BA.2 in March 2022, experts have warned this latest wave should not be underestimated or played down.
Here Yahoo News UK looks at why the is UK facing a new wave of COVID, and how bad it is likely to be.
The spread of BA.4 and BA.5
The new wave of infections is being driven by variants BA.4 and BA.5, which are types of the Omicron variant and currently make up more than half of new COVID cases in England.
BA.4 and BA.5 were designated as variants of concern on 18 May by the UK Health and Security Agency (UKHSA), on the basis that they appeared be more transmissible than previous Omicron sub-variants, including the previously dominant BA.2, which spread rapidly through the population in spring of this year.
According to the UKHSA, BA.5 is growing approximately 35% faster than BA.2, while BA.4 is growing 19% faster.
This means it is likely BA.5 will soon become the dominant variant in the UK.
Read more: Here are the most common symptoms of Omicron
The World Health Organization warned last week that the variants were driving a global rise in cases, with infections on the increase in 110 out of 193 countries.
According to the UKHSA, there is “currently no evidence” that the two variants cause more serious illness than previous types of Omicron.
The new BA.4 and BA.5 wave comes amid waning immunity in the population, both from prior infection and vaccination.
Currently, according to modelling from Cambridge University, around 30% of infections are reinfections, a proportion that is forecast to increase as the pool of people yet to catch COVID dwindles.
According to Meghan Kall, epidemiologist at the UKHSA, roughly 10 million people in England have never had COVID.
Declining population immunity is due in part to the fact that having caught the previous Omicron variant offers little protection against catching COVID again.
According to a study led by researchers at Imperial College London, published in June, this explains why repeat infections have become a common feature of Omicron waves.
Professor Rosemary Boyton, from Imperial’s Department of Infectious Disease and the report's lead author, said: “Getting infected with Omicron does not provide a potent boost to immunity against re-infection with Omicron in the future."
Professor Danny Altmann, from Imperial’s Department of Immunology and Inflammation, added: “We have found that Omicron is far from a benign natural booster of vaccine immunity, as we might have thought, but it is an especially stealthy immune evader."
Watch: New wave of Omicron mutations spreading across Europe, EU Medicines Agency warns
In addition, early studies suggest that vaccines offer less protection against infection from BA.4 and BA.5 than previous variants.
Research published in the New England Journal of Medicine on 22 June found that BA.4 and BA.5 "substantially escape neutralising antibodies induced by both vaccination and infection".
Dr Dan Barouch, of Harvard Medical School's Beth Israel Deaconess Medical Center and one of the report's authors, told CNN: "Our data suggest that these new Omicron subvariants will likely be able to lead to surges of infections in populations with high levels of vaccine immunity as well as natural BA1 and BA2 immunity.
"However, it is likely that vaccine immunity will still provide substantial protection against severe disease with BA4 and BA5."
Moreover, the bulk of the UK's booster campaign took place in December and January, meaning protection will have faded in the six months since many received their third dose.
Should we be worried?
While infections have risen rapidly in the last week, the rate of growth appears to be slowing. Cases leapt by 18%, down from 32% the week before, suggesting the peak of the spike may be approaching.
Hospital admissions on the other hand are rising rapidly – although are still well below levels recorded during the 2020 and 2021 waves.
On 4 July, England recorded 1,911 new COVID hospitalisations, up from 443 on 4 June.
The number of people in hospital in England who have tested positive for COVID stood at 11,878 on July 7, an increase of 33% compared to the previous week.
The majority of these patients are being primarily treated for something else other than COVID. However patients testing positive for COVID in hospital put huge strain on NHS resources due to stringent infection controls and the need to keep them separate from other people on the wards.
The number of people with COVID requiring mechanical ventilator beds stood at 232 on 7 July, up 10% compared to the week before and the highest number for two months.
Experts have raised concerns that cases are increasing among older age groups, which could further drive up hospital numbers.
Dr Kit Yates, mathematical biologist at the University of Bath and member of the Independent Sage group of scientists, said: "Cases are continuing to rise in all age groups as well.
"As always, of particular concern are the high prevalence levels in the oldest age groups who are most likely to suffer poor outcomes from COVID infection."
Around one in six people aged 75 and over in England – 16% – have not received a dose of a COVID vaccine in the past six months, putting them more at risk of severe disease.
COVID deaths have also increased, but are far below the levels recorded in previous waves.
According to the ONS, the number of deaths involving COVID in the UK increased from 309 to 346 in the week to 24 June, the most recent week for which complete data is available.
Deaths involving COVID accounted for 2.8% of all deaths that week, an increase from 2.5% in the previous seven days.
While the link between COVID infections and deaths has certainly been weakened by the UK's strong vaccine coverage, many experts are warning that the risk of Long COVID is being downplayed.
The latest ONS figures show an estimated 2 million people living in private households in the UK, the equivalent of 3% of the population, were experiencing Long COVID as of 4 June.
Dr Yates said: "That is a lot of people.
"This is why it isn't OK just to let everyone get infected as we are doing at the moment."
Aside from the risks posed by the illness, widespread COVID infections cause severe disruption to people's lives.
Staff absences continue to affect public services – including an already strained NHS, where workforce illness leads to to the cancellation of operations and creates even longer waiting lists.
Will any restrictions return?
It's extremely unlikely that the UK will enforce new COVID restrictions due to deep political opposition from the Conservative Party.
Outgoing prime minister Boris Johnson has staunchly opposed the return of restrictions, including during the wave of Omicron earlier in the year.
Some NHS hospitals have brought back mask policies as they deal with a resurgence in cases – though the advice is not legally enforceable.
The trusts say there is a need to protect staff and patients from falling ill, and more are expected to follow suit.
In the Autumn, everyone aged 65 and over will be offered a booster jab alongside frontline health and social care workers.
Reports suggest the rollout could be expanded to all over 50s.