April 4, 2007
Health officials are seeing stronger, tougher flu bugs this year. A new Japanese study now suggests that Influenza B is becoming resistant to two antiviral vaccines commonly used to protect against flu, zanamivir, marketed as Relenza, and oseltamivir, best known as Tamiflu.
Officials say the report is disturbing since health officials are counting on stockpiles of Tamiflu to control the early stages of any pandemic that might occur.
The study, conducted by Dr Shuji Hatakeyama, of the University of Tokyo, and scientists from various academic and government institutes, appears in the Journal of the American Medical Association (JAMA).
There has been previously documented evidence that some type A viruses have can develop a resistance to Tamiflu, but this is the first study to find a similar situation with type B viruses. Influenza B viruses are associated with annual outbreaks of illness and increased death rates worldwide, according to background information in the article.
The researchers collected influenza B isolates from 74 children before and after oseltamivir therapy and from 348 untreated patients with influenza (including 66 adults). Four hundred twenty-two viruses from untreated patients and 74 samples from patients after oseltamivir therapy were analyzed.
The researchers identified a variant with reduced drug sensitivity in one (1.4 percent) of the 74 children who had received oseltamivir, and seven (1.7 percent) of the 422 influenza B viruses isolated from untreated patients were found to have reduced sensitivity to zanamivir, oseltamivir, or both.
Review of the clinical and viral genetic information available on these seven patients indicated that four were likely infected in a community setting, while the remaining three were probably infected through contact with siblings shedding the mutant viruses. Continued surveillance for the emergence or spread of neuraminidase inhibitorresistant influenza viruses is critically important, the authors write. Further evaluation of the biological properties of neuraminidase inhibitorresistant influenza viruses is needed to fully assess their pathogenicity in humans.