The air re-circulation on planes has always been an issue, plus being so close to so many other human beings. And they keep the air super-dry, which dries out nasal passages and mucus membranes and makes them more susceptible to germs. Airplanes are always prime germ transmission machines. I would certainly avoid flying to any area where there is known Coronavirus, unlike someone I know who is flying to California this week.
Trains aren't quite as bad IMO because people aren't crammed quite so tight and there is a lot more circulation of fresh air. But still anyone who has to take any type of public transport needs to be very cautious about washing hands/using sanitizers, and wiping down phones, etc that may have been contaminated. I read an article about how you shouldn't be wiping down cellphones with sanitizer but I've been doing this for a long time and my phone is still working.
The number of articles I have read discouraging such precautions is ridiculous. Don't wear masks, don't wipe everything down, don't stay away from public transportation, it's all just hysteria they say. And yet they can't contain the virus.