Drug-resistant flu viruses increasing worldwide
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In the last decade, new research indicates, the proportion of influenza A viruses that are resistant to a primary influenza drug, adamantane, and its derivatives, has increased markedly worldwide—a trend researchers believe is “a cause for concern.”
Researchers in a second study provide another worrisome observation: flu vaccines are only modestly effective in elderly individuals. Both studies are reported in the September 22nd online issue of The Lancet.
Previous reports have suggested a low rate of resistance to adamantanes among circulating influenza viruses, Dr. Rick A. Bright, from the Centers for Disease Control and Prevention in Atlanta, and colleagues note. However, there has been an increase in the use of these agents globally in recent years and the impact on resistance has not been addressed.
In their study, Bright’s team evaluated the emergence of adamantane-resistant influenza in countries participating in the World Health Organization’s global surveillance network. Data from participating centers were submitted to the CDC for analysis between October 1994 and March 2005.
Over 7,000 influenza A virus isolates were tested for mutations known to confer adamantane resistance. Between 1994 and1995, just 0.4 percent of isolates were resistant to these agents. However, between 2003 and 2004, the percentage had skyrocketed to 12.3 percent.
Further analysis showed that 61 percent of the resistant viruses obtained since 2003 came from people in Asia, the report indicates.
“Our data raise concerns about the increasing incidence of adamantane-resistant influenza A viruses circulating throughout the world and draw attention to the importance of tracking the emergence and worldwide spread of drug-resistant viruses,” the authors conclude.
In the second study, Dr. Tom Jefferson and colleagues, from Cochrane Vaccines Field in Rome, conducted a systematic review of the literature to determine the efficacy of influenza vaccines the elderly. A total of 64 studies were included in their review.
The authors found that inactivated influenza vaccines were not significantly effective against influenza, influenza-like illness, or pneumonia in elderly subjects living in the community. However, there was evidence that vaccination helped prevent influenza- and pneumonia-related hospitalization and death.
In a related editorial, Dr. Yi Guan and Dr. Honglin Chen, from the Shantou University Medical College in China, comment that “the studies published today reinforce the shortcomings of our efforts to control influenza. For too long, the development and manufacture of influenza vaccines and antiviral drugs has been of limited interest to drug companies.”
A “wide-ranging approach” must be taken to prevent and control influenza epidemics. This should include increased surveillance, better use of existing influenza vaccines and drugs, the “development of new agents to boost our arsenal,” they add.
SOURCE: The Lancet, September 22, 2005.
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