Infrastructurist quotes from the government’s own reference guide, and indeed, flying is a swell way to spread viruses.
“A sneeze produces approximately 2 million viable particles. These do not remain airborne very long, but are highly infective and can be inhaled by people near the infected source. Talking can produce as many as 2,000 particles per explosive sound.”
Also, the low humidity on a plane flight is an ideal environment for viruses.