Any process in which a symbiont inhibits or disrupts a host ubiquitin-like protein ISG15 conjugation to a substrate. ISG15 is a ubiquitin-like protein that is conjugated to lysine residues on various target proteins. For example, some viruses escape the antiviral activity of ISG15 by using different mechanisms; the influenza B virus NS1 protein blocks the covalent linkage of ISG15 to its target proteins by directly interacting with ISG15, while the papain-like protease from the coronavirus cleaves ISG15 derivatives.
suppression by virus of host ISG15 activity