COVID-19 epidemic was predictably likely so countries cant say it was unexpected.

"First, the triggering event can be of natural or anthropogenic origins, or be the result of a combination of the two (ILC Commentary to  ARS, Article 23, §3. This source will be referred to as ‘Commentary’ in the rest of this post). There are two types of triggering events. The event can be an unforeseen one, in the sense that it is ‘neither foreseen nor of an easily foreseeable kind’ (Commentary, §2).  It would seem fair to say that the initial outbreak of the virus (SARS-CoV2) was unforeseen, but that some form of viral pandemic occurring in the next few years was foreseeable (see, here and here). Most States where the virus spread in the early days, when there was considerable uncertainty as to what was happening, may be able to rely on the event’s unforeseen nature. But this may not be the case for all. States where the virus has spread once the outbreak was known may not be able to rely on this limb of the triggering event: for them, the event would not have been unforeseen or unforeseeable."

Source :

COVID-19 and Defences in the Law of State Responsibility: Part I
Written by Federica Paddeu and Freya Jephcott

Blog of the European Journal of International Law