Fox news is misinforming readers.

Here's the preprint:

https://www.biorxiv.org/content/10.1101/2022.10.13.512134v1.full

TLDR: No, they reduced the deadliness of the original virus by 20%, by replacing the spike proteins with omicron spike proteins. Note that this deadliness is in a type of mouse engineered to be especially susceptible to CoVID, for use in these types of study: The results are not transferable to its effect on your normal mouse, so you should stop worrying about that. An needless to say a mouse is also dissimilar to a human, in its response to infection by CoVID.

1) You wonder if the dangerousness is related to the spike protein itself on the omicron variant of CoVID, as well as the main body of the virus.

2) So you make some mice that are genetically smooshed to be especially susceptible to SARS-CoV-2, by having them express a human version of Angiotensin-converting enzyme 2 (ACE2), and the human keratin 18 (K18) promoter, which makes the human ACE2 express in the epithelial cells.

3) Then you take 3 CoVID virus strains.
* The original strain from Wuhan.
* Omicron.
* A the original strain, but with the Omicron spike proteins instead of the original protiens. (For the interested, in the spike protein are 37 of the 59 differences between the original and omicron.)

The mice infected with the original die about all the time (6/6 transgenic mice)
The mice infected with omicron live (0/10 transgenic mice)
The mice infected with the hybrid strain die about 80% of the time (8/10 transgenic mice)