This most common type of flu has become nearly 100% resistant to two commonly used antiviral medications, according to disease control experts.

In previous years, amantadine and rimantadine failed against H3N2 (influenza A) between 2% and 15% of the time in North America. This season the number of resistant cases has climbed to more than 92%, according to a recent article in the New England Journal of Medicine.

Experts contend that this year’s flu strains are still responsive to two other antivirals, Relenza (zanamivir) and Tamiflu (oseltamivir). Also, flu vaccines continue to be effective, officials say.