Ghusl will pass on the virus so this is why it should not be performed.
People who wash deceased person[s] and then die themselves are not martyrs. Just like a person who does not eat anything haram then dies because of it. In a dire situation of life and death even pork can be consumed to save ones life.
The shariah is meant to protect life and not endanger it.
Also many people can be prayed over at once, this is permissible.