Resistance to anti-flu drugs has risen by 12 percent worldwide in the past decade, scientists said on Thursday in a finding that could pose problems for health officials trying to avert a pandemic.
Researchers at the Centers for Disease Control and Prevention found resistance to a class of drugs used to treat influenza for more than 30 years rose from 0.4 percent in 1994-1995 to 12.3 percent by 2004.
In some countries in Asia, where scientists suspect the next strain of flu with pandemic potential will originate, drug resistance exceeded 70 percent.
“Our report has broad implications for agencies and governments planning to stockpile these drugs for epidemic and pandemic strains of influenza,” said Dr Rick Bright of the CDC.
The findings, which are reported online by The Lancet medical journal, suggest the drugs amantadine and rimantadine will probably no longer be effective for treatment or as a preventive in a pandemic outbreak of flu.
The drugs, known as adamantane derivatives, inhibit the replication of the influenza A virus. But they do not work against influenza B viruses or the H5N1 strain of bird flu that has killed more than 60 people since late 2003.
Although it is not easily transmitted from person to person, public health officials fear the H5N1 strain could mutate and cause a worldwide pandemic.
Two other drugs, Roche’s Holding AG’s Tamiflu and GlaxoSmithKline’s Relenza which belong to another class called neuraminidase inhibitors, have been shown to reduce the severity of a flu infection and prevent it in some cases.
The World Health Organization recommends governments build stockpiles of neuraminidase inhibitors in case a pandemic develops.
The CDC researchers said their study of 7,000 influenza A viruses obtained worldwide is the largest and most comprehensive report on adamantane resistance to date.
The researchers did not explain why there was an increase in resistance.
About 5 percent to 20 percent of the population in the United States gets the flu each year, according to the CDC.
“Our data raise concern about the increasing incidence of adamantane-resistance 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 scientists said.
In a separate report that assessed 64 studies of the impact of flu vaccines in the elderly, researchers in Italy found the vaccines were not effective against influenza or pneumonia but prevented up to 30 percent of hospitalizations for pneumonia.
In people living in long-term care facilities the vaccines prevented up to 42 percent of deaths from the flu and pneumonia.
