What you may want to do is use Sanitizer Wipes, mini bottles of hand sanitizer and breathe through your nose and keep your mouth closed. Having a lot of Probitcics before and after the flight along with Emergen C before during and after the flight and other liquids will greatly reduce you getting sick. What you need to also do is walk up and down the aisles as much as possible to avoid contact with the sick passenger.

Also do not use the airline blanket or pillows. And be sure not to touch your face without washing your hands throughly with warm water. You could also politely tell the passenger to please contain his or her cough so as to void you getting sick.

Zinc losengers can be great as well as Echanacia and Godsend and Edelberry. Take these three days before, during and after your flight. At the first sign of a tickle up the zinc.

If you are that concerned you could ask the Flight attendant discreetly about your concern and she was she suggests.

Also pack Sailie Spray in your checked luggage and use it before you leave and then once you arrive take a warm shower and use it before going to bed. Sudafed/Mucinex or Antihistamine can also help you keep your airways open so you can breath through your nose. When you only breath through your nose and keep your mouth closed it works like an air filter. It has worked for me.