What strategy protect against the transmission of the flu virus?
clean your hands and surfaces often
practice safe food handling and preparation
refrain from engaging in sexual activity
visit the doctor regularly for check-ups

Clean your hands and surfaces often.

Explanation:

Flu virus can be transmitted through the process of inhale of droplets present in the air that actually consists of flue virus, also spread through contact with the respiratory secretions by the process of sharing utensils and  while handling of items contaminated by the infected person.  

A person must clean hands and surfaces so as to avoid infection with the flu virus which may be present on surface.