In a very important sense, it does not appear to be a stand-alone killer.

A mixture of ingredients is required for it to be part of a killing team. 

In the same way that the treatment for COVID-19 may require a cocktail of drugs, COVID-19 does not appear to be able to kill alone.

A good way to think about it may be like this. 

If someone pours gasoline all over you, it is not a good thing. But if you go home, throw away your clothes and take a shower, it is the end of the problem.

On the other hand, if someone strikes a match and throws it at you when you are doused with gasoline, it is a big problem.