What are the specific viruses cited as examples of novel threats never before documented to cause human illness?

Answer

SARS and COVID-19.

The emergence of coronaviruses responsible for Severe Acute Respiratory Syndrome (SARS) and COVID-19 fits the description of pathogens entirely new to humans.

What are the specific viruses cited as examples of novel threats never before documented to cause human illness?
diseasepathogenInfectionemergence