BRIEF OF THE DAY: Flu Virus Resistance to Tamiflu® Raises Concerns
CONTEXT:
On January 25, 2008 Norway notified the World Health Organization (WHO) of influenza A(H1N1) viruses showing a high rate of resistance to the antiviral drug oseltamivir (Tamiflu®). WHO then collected data from multiple participating laboratories in the Global Influenza Surveillance Network to determine the severity of the problem. So far, 20 countries report resistant versions of H1N1 flu viruses. Of 2,400 viruses gathered in 41 countries, around 13 percent carry the mutation that results in high-level resistance to Tamiflu®. Such resistance means that individuals treated with the drug are not likely to derive any benefit from the treatment. Tamiflu® resistance causes concern among health authorities worldwide since it is the most effective antiviral against H5N1 virus, known as avian flu. Public health experts think the H5N1 strain is the most likely flu virus to trigger a pandemic. Tamiflu® is the most commonly planned treatment for H5N1 infection among national and corporate plans for coping with flu pandemic. The H1N1 flu viruses are still treatable by zanamivir (marketed as Relenza), a drug in the same class as oseltamivir, and two older flu drugs, amantadine and rimantadine. The rate of H1N1 flu resistant viruses varies by country, with around 19 per cent resistant in Europe and a little over eight per cent in the United States and Canada. Previously the rate of flu viruses resistant to oseltamivir was under one per cent. Previous thinking on resistance of flu viruses to oseltamivir assumed that any viruses developing resistance to the drug would be weakened and fail to transmit from person to person. The current data shows that people who were not treated with Tamiflu® also carry resistant viruses. The European Centre for Disease Prevention and Control issued a statement that noted, "These are the first human influenza viruses resistant to oseltamivir found transmitting in the community anywhere in the world." H1N1 viruses comprise one of two subtypes of influenza A viruses circulating mostly in the winter. The mutation, called H274Y, observed in the recent data does not cause resistance in the other type of influenza A viruses, the H3N2 subtype. Authorities report no resistance has been found in influenza B viruses this season either. WHO continues to recommend use of Tamiflu® as the preferred treatment for attempting to contain ordinary flu and pandemic flu. Yet, some health officials report concern that use of the drug for ordinary flu will accelerate resistance to it and make it even less effective against pandemic flu. Brit Oiulfstad, the pandemic influenza coordinator for the County of Los Angeles, noted concern over “the current push for community-wide antiviral prophylaxis when the effectiveness for such long-term use (several times the duration of the recommended treatment period) has not been evaluated.” He added: “We do not know the effects of long-term antiviral use in a prophylactic setting. Therefore, we always consider that we must do no harm, and until we have some more answers, we proceed on those recommendations for prophylaxis with great caution. Until the science is in that shows that these drugs prevent illness, this seems to be the only reasonable way to approach the problem.”
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WHO Studies Tamiflu Resistance in Wake of New Report
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PREVENTION THOUGHT: Risk Management: Some planners considering how to mitigate the impact of pandemic flu express concern over the widespread use of antivirals contributing to the growing resistance of flu viruses. How would you assess the risk involved in continuing use of antivirals such as Tamiflu® in the prevention of ordinary flu considering it is the primary treatment planned for a pandemic flu outbreak?
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