The only portals of entry are the nostrils and mouth/throat. In a global epidemic of this nature, it’s almost impossible to avoid coming into contact with a flu virus in spite of all precautions..
While you are still healthy and not showing any symptoms of flu, in order to prevent proliferation, aggravation of symptoms and development of secondary infections, some very simple steps, not fully highlighted in most official communications, can be practiced (instead of focusing on how to stock N95 or Tamiflu):