Covid-19: New Delta variant strain detected in US after spreading across UK

A new strain of the Delta variant of Covid-19 that has been spreading across the UK has now been detected in the US, health officials said at a White House briefing.

The UK has seen more than 40,000 cases of Covid per day for eight days – now approaching 50,000 – and authorities have established a link with the new strain, called AY.4.2.

Experts Jeffrey Barrett, director of the Covid-19 Genomics Initiative at the Wellcome Sanger Institute in Cambridge, and Francois Balloux, director of the University College London Genetics Institute, told The Financial Times that they believe AY.4.2 is between 10 to 15 per cent more transmissible than the original form of the Delta variant – itself much more infectious than previous forms of Covid.

Speaking at the White House Covid Response briefing on Wednesday morning, Dr Rochelle Walensky, director of the Centers for Disease Control and Prevention, confirmed the presence of the new strain in the US.

Saying that it had “drawn some attention in recent days”, so far it has not been linked to any clusters of cases in the country.

“We have, on occasion, identified this sub-lineage here in the United States, but not with recent increased frequency or clustering to date,” Dr Walensky said.

“At this time, there is no evidence that the sub-lineage AY.4.2 impacts the effectiveness of our current vaccines or therapeutics and we will continue to follow.”

She added: “In the United States, Delta remains the dominant variant with more than 99.7 per cent of sequence cases in the country being caused by Delta.”

UK health officials say they are closely monitoring AY.4.2 after data last week linked it to six per cent of Covid cases in the country. So far, it has not been officially labelled as “under investigation” or a “variant of concern”.

The CDC told The New York Post that there have been less than 10 cases identified in the US – less than 0.05 per cent of those sequenced by labs.

There is no information on where in the US the strain has been detected.

Officials say that although it is important to monitor the development of new variants, there is nothing yet to indicate that this would develop into something so widespread that it would replace Delta as the dominant form of Covid.

The UK is being watched closely. Vaccination levels are high (67.6 per cent of the population of 67 million are fully vaccinated), and the vaccines have proven highly effective at preventing hospitalisation, or death – but still cases are rising, although not with the severity of earlier waves, pre-vaccine.

“While it [AY.4.2] may make things more difficult, it doesn’t by itself explain the recent high UK caseload,” Mr Barrett told The Financial Times.

It is believed that the spike in cases may be partially down to less enforcement of mitigation measures such as mask-wearing; less vaccination of teenagers compared to most other countries; and the waning efficacy of vaccines over time given that the UK was one of the first nations to roll out a program to the general population.

Medical authorities continue to underline the need for people to be vaccinated or receive a booster shot if eligible, to minimise the risk of infection, developing severe symptoms, or a fatal case of Covid.