Resistance to anti-flu drugs increases: study

LONDON (Reuters) – 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 (CDC) in Atlanta 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.