gain also means aquisition if you are not talking about signals the function of "lethality" was reduced in association with the recombination, thus attenuated

gain also means aquisition if you are not talking about signals the function of "lethality" was reduced in association with the recombination, thus attenuated in summary, if you look hard enough you may be able to find gains, but overall it is attenuation. this isnt the research you seem to be concerned about. you should be more concerned with codon scale editing of the nonstructural features of the virus as there is a direct influence upon interferon dynamics that is understood, and can be easily influenced by editing additional codons into the code at the "region" associated with interferon cascade mediated lethality. i will not give details here, but i you choose to look around and do some hard reading, you will discover, that the recipe for extremely lethal corona virus is not complex, but requires a lab capable of keeping and using the accesory biochemicals that allow primary sequence editing- that is to say any molecular genetics lab