A new highly contagious Covid variant could spark a wave of infections this summer, scientists have warned.

Dubbed 'Nimbus', the strain is descended from the already super virulent Omicron and has already triggered a surge in cases in China, Singapore and Hong Kong. 

Data from the UK Health Security Agency (UKHSA) also shows 13 cases of Nimbus, known scientifically as N.B.1.8.1, have already been detected in England. 

And 25 British samples of the strain have been submitted to an international Covid database since the end of March. 

However, both figures are likely an underestimation of how far the variant has spread given how testing has been massively reduced from the height of the pandemic. 

Other UKHSA data show the percentage of people testing positive for Covid has risen to its highest point this year, and is already 97 per cent higher than the level recorded in March.

Now, British scientists have warned Nimbus could lead to a surge in Covid cases in a matter of weeks, and have urged the vulnerable to get vaccinated.

They warn that many people's immunity to the virus, built up from previous infections and older jabs, has likely faded meaning they could be at higher risk of falling ill. 

Professor Lawrence Young, a virologist at Warwick University, said Nimbus had the potential to drive a surge in cases as the weather warms up and people become more sociable.

'We are very likely to see a spike of infections over the next couple of months, possibly by later this month or in July. But it’s difficult to predict the level of this infection wave,' he told The i Paper.

'Population immunity, either from vaccination or previous infection, is waning and, unlike other respiratory viruses such as flu, the Covid virus continues to spread in hot and humid weather,' he said. 

He added lab studies suggest Nimbus can infect human cells more efficiently than previous strains, and that it may have increased ability to dodge the immune system, making it more likely to infect people.

There is currently no evidence that the strain is more likely to cause severe illness or death in those it infects, compared to previous strains. 

However,  infection with the virus can still be deadly for more vulnerable groups. 

Covid was a factor in the deaths of just over 300 people in England in May, according to the latest official figures. 

Nimbus now accounts for 10.7 per cent of Covid infections worldwide, according to the World Health Organisation (WHO), compared to just 2.5 per cent a month prior. 

Last month the UN-body declared the strain a 'variant under monitoring'.

This means that the WHO is tracking the virus, watching for signs it could pose a significant threat to the public which would promote it to a 'variant of concern'. 

Experts have also said that current Covid vaccines, which have been reformulated to combat Omicron descendants, are expected to remain effective against Nimbus. 

Symptoms of Nimbus do not appear to differ from other Covid variants and include fatigue, fever, muscle ache and a sore throat. 

UKHSA data on Covid tests, which goes up to June 1, show 6.1 per cent of the people who were tested that week were positive for the virus, the highest figure for 2025 so far. 

This is a seven per cent rise from last week's figure and a 97 per cent increase from that recorded at the beginning of March. 

Dr Gayatri Amirthalingam, UKHSA's deputy director, said the organisation was keeping a close eye on Nimbus.

'UKHSA is monitoring all available data relating to SARS-CoV-2 variants in the UK and abroad, and we continue to publish our findings in our regular Flu and Covid-19 surveillance reports,' she said. 

'NB.1.8.1 has been detected in small numbers in the UK to date, but international data suggests that it is growing as a proportion of all Covid-19 cases.'

Currently adults over the age of 75, care home residents staff as well as people with a weakened immune system are eligible for a free Covid vaccine in Britain. 

UKHSA data suggests people who had a Covid jab as part of last spring's booster campaign were 45 per cent less likely to need hospital care for the virus in the weeks that followed compared to the unvaccinated.

The agency has urged all people eligible for a vaccine to get jabbed to protect themselves from both NB.1.8.1 and Covid in general.