A new report issued by the UK Health Ministry on Friday indicated an increase in the prevalence of a new offshoot of the Delta variant of Covid-19. The new Delta sub-lineage is known as AY.4.2. It’s more commonly known as “Delta Plus.”

In fact, the U.K. had its highest daily jump in cases Sunday compared to mid-July. There’s concern that the cases might be tied to the delta plus variant.

What is Delta Plus?

The Delta Plus variant is very similar to the original Delta variant, which is the dominant strain of Covid in the UK as it has been since May.

This new variant, scientifically named AY.4.2, was first identified in July.

Delta Plus was included in a UK Government briefing that summarised Covid “variants of concern and variants under investigation in England” published last Friday.

Delta Plus found in UK, US and Denmark

According to the BBC, AY.4.2 was discovered in 6% of Covid-19 samples tested in the week beginning September 27, according to the UK Health Ministry, which noted the offshoot’s “increasing trajectory.”

From the report:

This sublineage is currently increasing in frequency. It includes spike mutations A222V and Y145H. In the week beginning 27 September 2021 (the last week with complete sequencing data), this sublineage accounted for approximately 6% of all sequences generated, on an increasing trajectory. This estimate may be imprecise due to known sequencing issues affecting position S:145. Further assessment is underway.

Some 14,705 cases with this new variant have been reported in the country overall. According to CNBC, the United Kingdom currently has one of the highest rates of infection in the world.

According to the BBC, a small number of Delta Plus cases have been identified in the United States and Denmark.

AY.4.2 has been detected in five states: Washington, Oregon, California, North Carolina, and Washington, D.C., with seven cases reported overall.

According to another report, Israel discovered its first case of AY.4.2 today.

Most infectious Covid variant yet?

Professor Francois Balloux, director of University College London’s Genetics Institute, believes the Delta offshoot could be more infectious.

“Its trajectory in the UK hasn’t changed over the last 2 days,” Professor Balloux wrote on Twitter yesterday. “The increase also doesn’t seem region-specific, which may suggest A.Y.4.2 is intrinsically more transmissible, rather than being carried by a demographic event.” See chart below.

But Balloux warned that even an approximately 10% increase in infectiousness “does not explain much of the recent case rises in the UK. Assuming 10% higher transmissibility and a freq of 10% only translates in 1% additional cases per ~5 day viral generation interval.” The rise of cases overall in the UK since the end of July has been a staggering 85%.

However, a Downing Street spokesman said: “There’s no evidence to suggest this variant, which I think is the AY4.2 you are referring to, is more easily spread.

“There’s no evidence for that but as you would expect we’re monitoring it closely and won’t hesitate to take action if necessary.”

The spokesman downplayed reports that Delta Plus is 10% more infectious as “speculative”.

‘Urgent research’ into the delta plus variant

Former FDA commissioner Dr. Scott Gottlieb also tweeted about so-called Covid Plus on Saturday.

“UK reported its biggest one-day Covid case increase in 3 months just as the new delta variant AY.4 with the S:Y145H mutation in the spike reaches 8% of UK sequenced cases,” wrote Gottlieb. “We need urgent research to figure out if this delta plus is more transmissible, has partial immune evasion?”