Deltacron and Stealth Omicron are two sub-variants in news as Covid cases rise again.
As you can guess, the strains are related to variants you're probably familiar with already - Delta and Omicron.
However, what they are exactly, the differences between them and their prevalence in the UK and around the world aren't immediately apparent.
After Omicron cases peaked in January, Covid cases dropped then plateaued in Scotland.
Infections appeared to rise again from the end of February and cases numbers have been ticking up since, according to Public Health Scotland data.
As sub-variants related to Delta and Omicron develop, health experts are monitoring the strains.
So, what are the differences between Deltacron and Stealth Omicron - and what do we know about them so far?
What is Deltacron?
Deltacron is a recombinant virus - that is, a variant that contains genes from both Delta and Omicron.
A recombinant virus happens when a person is infected with more than one variant and their cells replicate together.
On March 8, scientists from L'Institut Pasteur in Paris sequenced the genome of Deltacron and shared it with GSAID, a global Covid database, which confirmed the strain as a variant.
The World Health Organisation (WHO) said on March 9 that it is "tracking and discussing" Deltacron.
How many cases of Deltacron are there?
Cases have been found in France, the Netherlands, Denmark and the US.
About 30 cases of Deltacron have been discovered in the UK according to the UK Health Security Agency, The Guardian reported.
The i newspaper reported that the first cases of person-to-person spread are expected to be confirmed this week.
What is Stealth Omicron?
Stealth Omicron is another name for BA.2, a fast-spreading subvariant of Omicron.
The strain was dubbed Stealth Omicron because it is more difficult for researchers to track using standard tests like PCRs.
Omicron has a mutation that scientists use to identify it, and because Stealth Omicron lacks this feature, it is more time-consuming to tell apart from other variants.
Stealth Omicron is also being monitored by the WHO.
How many cases of Stealth Omicron are there?
The strain has been reported in 40 countries.
According to the latest figures from the UKHSA on January 24, there are 1,072 genomically confirmed cases of Stealth Omicron in England.
Will Stealth Omicron become the dominant Covid variant?
Omicron is currently the dominant Covid strain.
In last week's update, the WHO indicated that Stealth Omicron is expected to overtake it.
The latest React-1 study by Imperial College London indicates that Stealth Omicron accounts for almost half of cases from swabs taken between February 8 and March 1.
BA.2 was identified in 47 percent of cases in England and almost 45 percent of cases in London.
Is Stealth Omicron more infectious or severe than Omicron?
In an update last Wednesday, March 9, WHO official Maria said Stealth Omicron is more infectious than BA.1, which is the dominant strain of Omicron.
As for Stealth Omicron's severity, Van Kerkhove said that there's no sign of a difference between Stealth Omicron and Omicron.
It is unclear if Stealth Omicron can reinfect people who have had Omicron, said Dr Abdi Mahamud, the WHO's Covid incident manager.
Researchers in Denmark, which experienced an early Stealth Omicron surge, found that the sub-variant was 1.5 times more infectious than Omicron in preliminary data.
It does not appear to be more severe according to early data.
"Initial analysis shows no differences in hospitalisations for BA.2 compared to BA.1," reported Statens Serum Institut, the Danish government's infectious disease research centre.
"It is expected that vaccines also have an effect against severe illness upon BA.2 infection."
Don't miss the latest news from around Scotland and beyond - sign up to our daily newsletter here.
