Drug Resistant Influenza
Medicine And Vaccines Are Becoming Ineffective Against The Flu Virus
Feb 13, 2008
The past two weeks has seen reports from Europe, Canada, and the United States regarding the appearance of drug resistant flu strains. The primary drug in question is Roche’s Tamiflu. The drug is expected to help halt the spread of a pandemic should it arise from the H5N1 strain of bird flu. Amidst the resistance and widespread outbreaks are reports of emerging flu strains in the population that are not covered by this year’s vaccine.
Common Flu Virus Strains
The flu is caused by the influenza virus. Several strains are known, the most common in circulation being influenza A subtypes H1N1 and H3N2 as well as influenza B types. Influenza B is found mainly in humans. Influenza A types sometimes also circulate in animals such as pigs and birds. The subtypes are categorized based on the surface proteins known as hemagglutinins (H) and neuraminidases (N). According to the Centers for Disease Control (CDC) there are 16 H types and 9 N types.
Developing Drug Resistance
As reported by Reuters, the drug maker claims that the limited use of its product for treating the flu has always been known. The nature of the virus and its ability to mutate and adapt makes it necessary to consistently pursue new treatments. Resistance to treatment by the common H1N1 strain has been reported in 8% of tests by the CDC in the United States and roughly 6% of tested samples in Canada. More than a dozen European countries found as much as 70% resistance, 14% on average, with Norway finding 12 out of 16 samples positive. Previous estimates of resistance were at less than a percent. The adaptation is suggested to be due to a single mutation and does not produce a more severe infection.
Tamiflu is being stockpiled by several governments to be used in the case of a bird flu pandemic in the human population. Made in Switzerland by Roche and referred to medically as oseltamivir, it is an antiviral medication widely used to treat viral flu. There are currently no reports in Asia about increased resistance of common strains to the medication though previously two strains of H5N1 bird flu exhibited resistance in the past couple of years.
In addition to oseltamivir, three additional drugs are FDA approved for treating the flu. The medications include the adamantadines amantadine and rimantadine as well as zanamivir. Resistance to the adamantadines, approved to treat A viruses, has been previously found and their use in the United States is no longer recommended. The neuraminidase inhibitors Tamiflu and zanamivir are both approved to treat all the common flu strains, both A and B types.
Lack of Protection by Vaccine
Each flu season the influenza vaccine, which protects against viral flu, is developed to protect against variations of the H1N1, H3N2, and influenza B strains that are expected to occur that year. About 30% of the H1N1 strain emerging this year is a variation that arose in Australia too late in the year for it to be included in 2007-2008 vaccine. There is also some question as to how well the B strains fit this year’s emerging strains. This will limit the vaccine’s effectiveness at preventing the disease, but will still offer some cross protection. The cross immunity is expected to keep the course of the infection more mild with less severe complications.
