can swine flu effects the person who already got treatment of tamiflu?

This is from http://www.drugs.com/tamiflu.html

"Tamiflu is an antiviral medication that blocks the actions of influenza virus types A and B in your body.

Tamiflu is used to treat flu symptoms caused by influenza virus in patients who have had symptoms for less than 2 days. Tamiflu may also be given to prevent influenza in people who may be exposed but do not yet have symptoms. It will not treat the common cold."

So in answering your question, if you have been exposed to Swine Flu (been in contact with someone diagnosed with swine flu) but don't have any symptoms yourself, you can be given Tamiflu so as to prevent you from developing Swine Flu.