Tamiflu, the most commonly used influenza antiviral drug and the key to the government's emergency stockpile, no longer works on the flu strain that is emerging as the most dominant in the U.S. this year. One flu expert says "We’ve never lost an antimicrobial this fast. It blew me away.”
Tamiflu became the more popular drug because it can be taken orally in pill or liquid form, whereas Relenza must be inhaled and can't be used by young children or the elderly.
What mystifies infectious disease experts and microbiologists is that the Tamiflu-resistant strain now circulating appears to be a mutation that spread naturally, not as a response to antiviral use.
"We don't think it's due to overuse," said Dr. Anthony Fiore, a CDC epidemiologist. "There's not as large amount of use of oseltamivir as there might be with antibiotics."