Why the new FLiRT group of variants is expected to bring a new wave of Covid

A new group of Covid variants is spreading fast, putting the UK at risk of a fresh wave of infections in the coming weeks, scientists warn.

Cases involving the variants, nicknamed FLiRT, have soared this month to account for around a quarter of total UK Covid infections.

They are replacing JN.1, the dominant variant they are descended from, that until recently accounted for virtually every case of the virus in the UK.

At the moment, the new variants appear to be largely replacing JN.1 rather than driving up Covid cases overall – which remain at around three year lows.

But there are fears that its continued spread could start to push overall cases higher, given that it seems to be more contagious and that vaccines don’t work as well against it, scientists say.

At the same time, the immunity the British public has built up from vaccines and previous infections is likely to be waning after several months of very low levels of the virus.

“It is likely we are about to enter a new wave of infections due to the global increase of new subvariants of the current dominant variant JN.1,” said Professor Christina Pagel, of University College London.

“I expect prevalence to increase in the coming weeks as we see the arrival of new variants that seem to be replacing the JN.1 variant that caused the Christmas 2023 wave.”

“Essentially, JN.1 has mutated further and several of its children have found mutations that help them spread much faster than their parent,” Professor Pagel explained.

The FLiRT variants involve two key mutations from the JN.1 virus which mean it can spread more easily.

One sees a mutation, known as F, being replaced by another, known as L. The other involves mutation R being supplanted by mutation T – giving the main letters for the term FLiRT.

Although some scientists are expecting a new wave, they predict that it will be considerably smaller than that seen in the run-up to Christmas last year, when more than 2.5 million, or 4.6 per cent of the UK population had Covid.

That’s because the new subvariants are not as different from their ‘parents’ some previous subvariants were from theirs, while the two mutations have been around before, earlier in the pandemic – but not since JN.1 became the dominant variant.

As such, the population may have some enduring immunity to those mutations but its hard to be sure, scientists say – as effect of any given mutation varies according to the variant it’s found in and is difficult to predict.

Professor Pagel said: “When the JN.1 wave hit around the world last December, it was significantly different to previous circulating variants and caused a substantial wave. Since these new FLiRT offshoots are more similar to JN.1, and we are heading into summer, hopefully any wave caused by these new subvariants will be smaller.”

Other scientists believe there is a risk that FLiRT could cause a spike in cases – although there is a good deal of uncertainty about whether this will happen and how big any outbreak may be, other than that is is likely to be smaller than the last wave.

Professor Lawrence Young, a virologist at Warwick University, said: “One FLiRT variant now accounts for 1 in 4 of all Covid infections in the US and so it is possible that these variants will cause a small wave of infection over the next few months.

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“These mutations have been seen before in previous Covid variants but not in the context of JN.1. This makes it difficult to predict the behaviour of the FLiRT variants as many folk will have some immunity due to previous infections.

“As the FLiRT variants are derived from JN.1 it is also likely that previous JN.1 infections will provide some protection. Recent data suggests that a previous JN.1 infection will provide good protection but that the modified booster vaccines currently available are unlikely to be effective against FLiRT variants,” he said.

Professor Eric Topol, of the Scripps Research Translational Institute in California, believes FLiRT could deliver “a wavelet but not a significant new wave of infections”.

He argued that these new subvariants are not sufficiently different from their parents to overwhelm the immunity people have collectively built up.

Paul Hunter, professor in Medicine at the University of East Anglia, said: “While we don’t know for sure, I doubt that we will see a major wave over the next few months. My guess is that infection and hospitalisation rates will probably decline further as we move into the summer, but probably slowly rather than any dramatic fall.”

“With the exception of 2022, when there were serial waves associated with new Omicron subvariants, there has been fairly strong evidence of “seasonal forcing” of Covid infections from the very first year,” said Professor Hunter, a member of the National Institute for Health Research’s Health Protection Research Unit, which contributed to national and international panels, including Sage and NERVTAG during the pandemic.

Whatever the size of any wave, scientists urge the public to take up the offer of a spring booster, if they have one – and for others to consider a private jab if they can afford it.