Two studies find flu treatments fall short

Updated Thu. Sep. 22 2005 11:34 PM ET

CTV.ca News Staff

Just weeks ahead of flu season and amid worries of a global influenza pandemic, come two new studies suggesting that our flu treatment and prevention methods may not be enough.

The first is a meta-analysis of 37 years of research which found that flu shots may not be as effective in preventing the illness in the elderly as commonly thought. The second study found that many influenza viruses have developed high rates of resistance to our most common antiviral drugs.

The first meta-analysis was done by a large group of scientists, known as the Cochrane Review Group, who looked at the results of 64 international studies and published their findings Thursday on the website of The Lancet medical journal.

They found that flu shots reduced by 27 per cent the chance of an elderly person ending up in a hospital with influenza or pneumonia.

The results were better when the elderly lived in nursing homes. There, the vaccines prevented up to 42 per cent of influenza and pneumonia deaths.

The study's leader, epidemiologist Dr. Tom Jefferson, says that there is "a wild overestimation" of the effectiveness of flu shots.

"It is assumed to be 70, 80 or 90 per cent in the elderly,'' Jefferson said, but the study shows "it's not as effective... That needs to be clearly presented to our customers, not fudged.''

The findings are similar to those of a previous study done by the U.S. National Institutes of Health that found flu shots for the elderly in the United States had not saved lives.

"The studies published today reinforce the shortcomings of our efforts to control influenza," wrote Dr. Guan Yi, a virologist at the University of Hong Kong, in an editorial that accompanied the study.

However, many health officials still say older people should be vaccinated. The World Health Organization and the U.S. Centers for Disease Control said the findings do not change their recommendation that elderly people should get the shot every year.

Flu drugs lost efficacy

Meanwhile, a second study, also published Thursday on The Lancet website, found that human flu viruses are becoming increasingly resistant to the class of drugs known as adamantanes, one of only two existing classes of flu drugs.

The authors of that study, conducted by researchers from the Centers for Disease Control and Prevention in Atlanta, say their findings call into question the future usefulness of the adamantane or M2 inhibitor drugs.

"We were alarmed to find such a dramatic increase in drug resistance in circulating human influenza viruses in recent years," said Dr. Rick Bright of the disease control centers. "Our report has broad implications for agencies and governments planning to stockpile these drugs for epidemic and pandemic strains of influenza."

What may be most worrisome is how quickly the flu viruses have become resistant to medicines once they are put into common use.

Before 2000, almost no virus was resistant to Amantadine. By 2004, 15 per cent of influenza A viruses collected in South Korea, 70 per cent in Hong Kong and 74 per cent in China were impervious.

Resistance rates were also high in a number of countries in South and Central America and in Europe.

In Canada, 30 per cent of viruses collected in 2005 and analyzed by the team were resistant to the drugs.

But infectious disease specialists say it doesn't change the message about the value of vaccinations.
 
"Even though it doesn't prevent all illnesses, it is effective at preventing serious illness and death," said Dr. Allison McGeer, head of infection control at Toronto's Mount Sinai hospital.

And then of course, there's the bird flu strain that has been ravaging poultry populations in Asia. In the few dozen cases in which humans have come down with the strain (H5N1), anti-viral drugs have been utterly ineffective.

The study's authors can't say why the viruses are becoming resistant but they speculate that it may be because of high use of the drugs in parts of Asia, where they can be bought without prescription, or because of a spontaneous mutation of the viruses.

Canada's Public Health Agency has plans to add large quantities of Amantadine to our pandemic stockpile. That's because the M2 inhibitors are much cheaper than the patent-protected neuraminidase inhibitors oseltamivir (Tamiflu) and zanamivir (Relenza).

But the CDC study authors warn governments that amantadine "will probably no longer be effective for treatment or prophylaxis... in the event of a pandemic outbreak of influenza."