The flu, like a cold, is a respiratory infection but is caused by an entirely different group of viruses - namely the influenza A, B and C viruses. Perhaps the best way to prevent the flu is to get an annual flu shot before the flu season hits.
I called Lufthansa, and they told me that there are Economy Plus seating sections on the Bangalore to Frankfurt and Frankfurt to Chicago legs. But, since I bought tickets through United, they told me I can't get any seat assignments until check-in in Bangalore unless I work with United.
Each different type of aircraft has a capacity for different amounts of seats. Some airlines reduce the amount of seats on the aircraft so as to provide more space for higher paying passengers. For example: Jetstar has 335 seats in their Boeing 787-8 Dreamliner. United has 219 seats in their Boeing 787-8 Dreamliner.