Flu has always presented a moving target for developers, with rapid evolution keeping viruses one step ahead of vaccines. In pandemic flu, mutations could turn a relatively benign virus into one that is more virulent, capable of spreading from human to human or resisting drugs.
Evidence is emerging that H1N1--the virus behind the 2009 influenza pandemic--is undergoing this mutation process. During the pandemic, governments turned to the Roche ($RHHBY) antiviral Tamiflu to treat patients. But data presented by a World Health Organization (WHO) collaborator shows one in 50 cases of swine flu are now caused by a Tamiflu-resistant strain of H1N1. The finding adds to earlier evidence that H1N1 was changing to overcome the antiviral.
Previously detected Tamiflu-resistant strains--which are caused by a single gene mutation--were less likely to spread than other forms of the virus. The mutation now being found appears to have overcome this limitation, though. An increasing proportion of patients with Tamiflu-resistant H1N1 have never been treated with the antiviral, suggesting that the mutated strain is spreading among people.
Having identified the trend, the focus is now on monitoring its rise. "Sustained global monitoring for the emergence of resistance is important to underpin public health and guidance for clinical management," WHO collaborator Aeron Hurt told The Guardian. Hurt--who presented the data this week in Australia--singled out patients who are immunocompromised, seriously ill in hospital, or not responding to antiviral therapy as needing particular attention.
With other recent research papers linking H1N1 vaccines to increased incidence of narcolepsy and Guillain-Barré syndrome, the small arsenal of pandemic flu defenses is now under attack.
GlaxoSmithKline's ($GSK) Relenza, an alternative to Tamiflu, is effective against the mutant strain but was less widely stockpiled as it is delivered by inhalation. If Tamiflu resistance becomes more widespread, Relenza may have to take up the slack. Some feel healthcare policies have raised the likelihood of this happening. Back in 2009, Dr. Tom Jefferson of the Cochrane Collaboration called the use of Tamiflu against seasonal flu "more than madness," and warned of resistance.