Especially this season flu cases are far lower than the previous year, and other antiviral drugs are working well against this particular flu virus and health officials are attentive to the current situation.

The cause of the mutation, which has made this virus resistance to that particular drug is still unknown, experts though, it occurred by the extensive use of Tamiflu in most of the country to treat RTIs (Respiratory Tract infections).

Last year, certain types of flu H1N1 viruses were get resistant to oseltamivir. Cases were reported from Europe and other countries.

This year, the U.S. Centers for Disease Control and Prevention was bewared for flu resistance to Tamiflu in the U.S and were expecting the resistance of virus to Tamiflu. Furthermore, the ratio of the resistant strain has grown up to 10 percent than the previous year to all of the H1N1 strains this year.

“The rising resistance of H1N1 influenza strains to antiviral drugs was first noted a few years back,” Imperato said. “Now, based on current analyses of H1N1 isolates from 16 countries in 2008, almost 31 percent showed resistance to Tamiflu.”

Tamiflu is still effective against the two other influenza strains, H3N2 and influenza B, for avian influenza (H5N1), affecting human beings Imperato said.

Flu causes almost 36,000 deaths, each year only in U.S. Most of the victims are elderly or those with any chronic disease such as asthma or cardiovascular disease. Bilateral Pneumonia resulting from flu is one of the fatal complications of influenza species.