Homeland Security - terrorism, contagious diseases, aviation sector

Over the years since 9/11, there has been a number of safety and security issues in homeland security sector.  Most have been terrorism related dealing with a multitude of groups.  Pandemics and surrounding health issues date back as 3,000 B.C. in "Hamin Mangha;" one of the best-preserved prehistoric sites in northeastern China. How ironic that we are now dealing with the COVID-19 virus which originated in the Wuhan, China not to include the Asian flu of 1957-1958. With that being said, do you foreseen the greatest threat to homeland security in the aviation sector to be terrorism or contagious diseases and why?