A new class of influenza drug has been shown by researchers to be effective against drug-resistant strains of the virus.

Researchers from the University of British Columbia led a study that was published on Thursday, Feb. 21 in the journal Science Express, explaining their development of a new drug candidate that stops the flu virus from spreading from one cell to the next.

The drug successfully treated mice exposed to lethal strains of the flu virus that were resistant to two flu antivirals that are currently on the market.

The flu virus spreads in the body by using a protein called hemagglutinin, which binds to the receptors of healthy cells.

After replicating in the healthy cell by inserting its own RNA, the flu virus emits an enzyme called neuraminidase that severs its connection, allowing it to move on to the next healthy cell and repeating the process.

This video shows the flu virus at work:

How the Drug Works: A "Broken Key"

"Our drug agent uses the same approach as current flu treatments -- by preventing neuraminidase from cutting its ties with the infected cell," says UBC Chemistry Prof. Steve Withers, the study's senior author. "But our agent latches onto this enzyme like a broken key, stuck in a lock, rendering it useless.

"By taking advantage of the virus's own 'molecular machinery' to attach itself, the new drug could remain effective longer, since resistant virus strains cannot arise without destroying their own mechanism for infection."

By directly interfering with the "key" enzyme mechanism of the influenza virus, Withers expects that this new drug can overcome the quick adaptation of the virus that allows it to become resistant to successive generations of flu vaccines.

The World Health Organization estimates that influenza affects three to five million people globally each year, causing 250,000 to 500,000 deaths. In some pandemic years, the figure rose to millions.

"One of the major challenges of the current flu treatments is that new strains of the flu virus are becoming resistant, leaving us vulnerable to the next pandemic," says Withers, whose team includes researchers from Canada, the UK, and Australia.

Currently available antiviral flu drugs like Relenza and Tamiflu also work by attaching to the neuraminidase enzyme, but the new class of drugs, called DFSAs, permanently attach to the enzyme in a way that keeps the flu virus from evolving further without inactivating itself.

The researchers showed that DFSAs work against both A and B influenza types, along with other known resistant flu strains.

When Can You Use It?

They are now conducting tests in other animals, in preparation for a version safe for humans to use.

Co-author Dr. Andrew Watts from the University of Bath told BBC News: "Our drug can work even better in drug resistant strains than in natural viruses emphasizing that it is working through a totally different mechanism."

According to Dr. Watts, it may take six to seven years before the drug is available to market.