Is UK headed for new Omicron wave? Experts warn waning immunity could drive fresh cases

One in 20 people were infected with Covid during the week ending 12 March

Covid cases are rising across the UK after a steady decline since January, new figures suggest (Jeff J Mitchell/Getty Images)

The UK has seen a recent uptick in Covid cases and hospital admissions after numbers had been falling steadily since the wave of Omicron cases in January.

After several weeks of decline, the latest NHS Test and Trace figures show that 323,032 people in England tested positive for Covid between 3 and 9 March, an increase of 55.5 per cent compared to the previous week where 207,728 people tested positive.

The Office for National Statistics (ONS) reported that roughly one in 20 people in England were infected with Covid in the week ending 12 March, an increase from one in 25 the previous week.

In Wales, an estimated one in 25 people had Covid during the same week, up from one in 30 the week before. In Northern Ireland, the number of cases slightly decreased from one in 13 the week before to one in 14, and in Scotland, they rose from one in 18 to around one in 14. According to government figures, 607,737 Covid cases have been reported in the last seven days across the UK.

The latest data from NHS England shows a similar trend with hospital admissions, with daily Covid admissions on a steady decline from a high of 2,317 at the end of December 2021, falling to 786 by the end of February this year.

However, admissions have now started to rise again. Since 28 February, daily admissions to hospitals in England have been consistently above 1,000, with 2,054 people admitted on 15 March.

Although experts were initially unsure what caused the rise in Covid cases and hospitalisations, they have now suggested it could be the result of waning immunity. More than two-thirds of the UK population aged over 12 have received a booster dose of the vaccine and 85 per cent have received at least two doses, with some countries thinking of administering additional boosters.

Experts have also credited a variation of Omicron, BA.2, for the rising Covid cases and hospital admissions. This sublineage of Omicron spreads more rapidly than the original variant, now known as BA.1, with “30 per cent more transmissibility”, but whether it causes severe illness is still unknown.

BA.2 was first detected in December last year, after the original Omicron variant led to a large wave of infections over the winter and put increased pressure on hospitals. It also led to widespread Covid cases around the world at the beginning of the year.

Eric Topol, professor of molecular medicine at the Scripps Research Institute in California, told The BMJ: “I would attribute this to the ‘BA.2 triad.’ The variant has 30 per cent more transmissibility than BA.1, but spread has been further enhanced by relaxed mitigation measures and waning of vaccine immunity.”

He added that this would further prolong the pandemic, causing “widespread surges” and potentially “another path to a new variant in the months ahead”.

However, according to Colin Angus, senior research fellow at the University of Sheffield’s school of health, there are two factors that will determine whether the rise in cases and admissions is just a “small bump in the road or a full-blown second Omicron wave”.

The first is how much people have relaxed their behaviours since Covid restrictions were removed in the UK at the end of last month. The second is the extent to which BA.1 infection provides protection against BA.2.

Although the UK government has removed nearly all Covid-related restrictions, experts are urging the government to be “careful” as the pandemic is far from over.

Simon Clarke, associate professor in cellular microbiology at the University of Reading told The BMJ: “The government must be careful not to dismantle all the systems which have allowed UK planners to stay ahead of the omicron wave through a successful vaccination drive.”