Elderly people — especially those living on their own — get much less benefit from flu shots than previously thought, a new study shows.

Whether this is good news or bad news depends on your point of view. The bad news for elderly people is that flu vaccination doesn't work as well as anyone would like. The good news for elderly people is that it does offer significant protection against complications from the flu such as pneumonia, hospitalization, and death.

The new findings come from a review of nearly every existing flu-vaccine study. Tom Jefferson, MD, and colleagues at Cochrane Vaccines Field in Alessandria, Italy, conducted the review. They report the findings in the early online issue of The Lancet.

"In the community setting, these influenza vaccines have a modest impact," Jefferson tells WebMD. "We could argue whether 26 percent protection against hospitalization is 'modest' or 'weak' — these are relative terms. People always give very high effectiveness figures for influenza vaccination: 75 percent, 80 percent, 90 percent. But these figures are variable according to the people, the setting, and the viruses circulating at the time. We tried to account for all of this."

Meanwhile, a CDC report in the same issue of The Lancet warns that circulating human flu bugs are very quickly becoming resistant to two older-type flu drugs: Symmetrel and Flumadine. The findings "raise concerns" about the widespread use of these drugs, note Rick Bright, PhD, research scientist at the CDC's National Center for Infectious Diseases, and colleagues.

"We notice over a brief time period an increase in the resistance rate," Bright tells WebMD. "The rate of increase is large and important, but not surprising."

CDC to Elderly: Get Your Flu Shots Anyway

Despite the new findings on vaccine efficacy, the CDC still advises everyone — especially the elderly — to get a flu shot every year. Why? Flu vaccine keeps many elderly people from getting really sick, says CDC spokesman Tom Skinner.

"This study and a number of other studies show the flu vaccine is effective in preventing serious complications that lead to hospitalization and death. We should not lose sight of that fact," Skinner tells WebMD. "We will continue to stress the importance of people in high-risk groups of getting vaccinated every year. Our hope is people won't get dissuaded from getting vaccinated by these studies showing various degrees of efficacy."

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Elderly in Long-Term Care vs. Elderly in Community

Jefferson and colleagues found that when researchers study how well flu vaccines work in the elderly, their findings are all over the map.

One reason is that flu is a tricky disease to track, says flu expert John Treanor, MD, of the University of Rochester in New York. Unless researchers actually analyze blood from people who get ill, it's hard to tell whether a flu-like illness is really the flu or another bug that causes flu-like symptoms.

"Most of these studies can't differentiate between illness caused by flu and other things, so they underestimate the effects of the vaccine," Treanor says. "It looks to me that what the Jefferson team saw is that, in elderly people, most studies find that flu vaccination protects against hospital admissions for pneumonia and death. And that is good."

You might expect flu vaccine to seem more effective in years when there are many flu cases out there, and when the vaccine is a good match for the virus. But that's not always the case.

"It is shocking to see that you have such contrasting evidence," Jefferson says. "Sometimes the vaccine works better when there is high virus circulation. But in some cases the reverse is true. The lesson is this is a far more complex, far more difficult problem than we have thought."

Jefferson and colleagues found that flu vaccination works better for elderly people in long-term care than for elderly people in the community.

For elderly people living in long-term care, flu vaccine was:

—Not effective in preventing confirmed flu

—23 percent effective in preventing flu-like illness

—46 percent effective in preventing death from flu or pneumonia

—45 percent effective in preventing hospitalization

—60 percent effective in preventing death from all causes

For elderly people living in the community, flu vaccine was:

—Not effective in preventing confirmed flu

—Not effective in preventing flu-like illness

—Not effective in preventing pneumonia

—26 percent effective in preventing hospital admission for flu and pneumonia

—42 percent effective in preventing death from all causes

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Why the Difference?

"In homes for the elderly, where you have a spread of different ages and different pathologies, vaccination had a slightly higher impact on influenza," Jefferson says. "But there may be other factors in play. Like the fact you have health care workers who will care for these patients, and also do personal hygiene. And other personal supportive measures, such as better diet, probably have an impact as well."

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A Call for Change

Jefferson says these findings point to an inescapable fact: The decades-old technology for producing flu vaccines is obsolete.

"What we have got here is a technology which does not work very well in the elderly. It doesn't work in children under the age of 2 years and has low effectiveness in adults and older children. What does that tell you?" Jefferson asks. "The idea you are going to prevent or contain a syndrome caused by hundreds of different agents mostly unknown at the time they are circulating with a single vaccine aimed at a tiny portion of these agents is a nonstarter. I hope our study illustrates that."

Jefferson calls for investment in new vaccines and a rethinking of how best to prevent serious flu-like illnesses.

Treanor agrees that more research — and new ideas — are needed.

"This does help put a focus on the basic truism of flu vaccination for the elderly: It works but it is not perfect," he says. "And we need to concentrate on other methods, which could include vaccinating contacts of the elderly, including children and health care workers. Maybe the best way to prevent flu in the elderly is to vaccinate everyone else. This is being actively considered."

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Fast-Rising Flu-Drug Resistance

There are two kinds of drugs that prevent flu and, if taken soon after infection, reduce the severity and length of symptoms.

There are two members of the older class of flu drugs: Symmetrel and Flumadine. The CDC is tracking how well the drugs work. Recently, there has been a huge spike in the number of circulating human flu bugs resistant to these two drugs.

Bright and colleagues analyzed more than 7,000 flu bugs from all over the world. Resistance to the older flu drugs increased from nearly zero in 1994-1995 to 12.3 percent of all viruses in 2003-2005.

In the U.S., there's been a sudden spike. In the first part of 2005, 14.5 percent of flu bugs were resistant to the two drugs — up from only 1.9 percent in 2004.

Perhaps of even more concern is that 74 percent of flu bugs in China are resistant to the two drugs. In Asia as a whole, 27 percent of flu bugs are resistant. Most experts say that if a new flu bug arises, it will come from Asia.

Even though they are old, Symmetrel and Flumadine are important for controlling flu epidemics, Bright says.

"Both the old and new classes of antiviral drugs are very important to controlling circulating strains of flu," Bright says. "Both classes have primary uses in different populations. It is part of a comprehensive strategy for flu control."

One issue is that the drugs are sold over the counter in some parts of the world — making inappropriate use more likely. But overuse isn't the only thing going on. For some reason, the resistant bugs seem to be popping up on their own.

Flu expert Treanor has never seen anything like it.

"This certainly looks like a real trend," he says. "It is hard for me to visualize exactly what might be going on here. The biology of flu is such that it is hard to understand why this resistance mutation might become fixed among circulating viruses. It is just a very interesting phenomenon."

The bird flu that has experts so worried about a killer flu pandemic already is known to be resistant to these two drugs. Fortunately, it remains resistant to the newer drugs Relenza and Tamiflu. And the bird flu virus is not spreading among humans.

It had been hoped that if the bird flu recombined with a human virus, it would become sensitive to the older flu drugs. The new findings show that it might not be a good idea to count on this.

By Daniel J. DeNoon, reviewed by Brunilda Nazario, MD

SOURCES: Jefferson, T. The Lancet, published online Sept. 22, 2005. Bright, R.A. The Lancet, published online Sept. 22, 2005. Tom Jefferson, MD, Cochrane Vaccines Field, Alessandria, Italy. Rick Bright, PhD, research scientist, National Center for Infectious Diseases, CDC, Atlanta. Tom Skinner, spokesman, CDC, Atlanta. John Treanor, MD, professor of medicine and director, vaccine and treatment evaluation unit, University of Rochester, N.Y.