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.
Please be aware that seat reservations on flights that are not operated by Lufthansa, Lufthansa Regional or Austrian Airlines may only be possible to a limited extent, or not at all, especially in Economy Class. Please contact the airline operating your flight.