[NVIC] Flu Death Risk,Vaccine Benefit Exaggerated

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BL Fisher Note:

Hopefully, this well researched, enlightened article about flu and

vaccination is a sign that the Washington Post has decided to engage in more

balanced reporting of the benefits and risks of vaccination. An intelligent

examination of the strengths and weaknesses of methodology used in various

kinds of scientific research is a step in the right direction. It serves as

a counterweight to the rhetoric used by some doctors and public health

officials who believe that fear and intimidation is the only way to control

the behavior of people.

http://www.washingtonpost.com/wp-dyn/content/article/2005/10/22/AR2005102200

042.html

The Washington Post

Tuesday, October 25, 2005; Page HE01

A Shot of Fear

Flu Death Risk Often Exaggerated; So Is Benefit of Vaccine

By Woloshin, M. Schwartz and H. Gilbert Welch

Special to The Washington Post

Medical research often becomes news. But sometimes the news is made to

appear more definitive and dramatic than the research warrants. This series

dissects health news to highlight some common study interpretation problems

we see as physician-researchers and show how the research community, medical

journals and the media can do better.

For years, the public health community has used fear as one strategy to

promote the flu vaccine. A vaccination poster distributed by the U.S.

Centers for Disease Control and Prevention (CDC), for example, emphasizes

that " 36,000 Americans die of flu-related illnesses each year, " implying

that the vaccine could prevent many of these deaths.

When it became aware of the vaccine shortage last October, the federal

government changed course and tried to reassure Americans that going without

a shot was no big deal. " We all need to take a deep breath. This is not an

emergency, " CDC director Gerberding advised the public.

Instead of urging vaccination for everyone age 50 and older, as they had

been doing, government officials recommended shots only for people 65 and

older, and those in selected high risk groups. The public's response was

predictable: People were upset and confused. Our local television news

played a story in which a pharmacist was called " a murderer " when his

vaccine supply ran out. Ironically, the crisis mentality led some to engage

in behaviors that probably increased their risk. Frail elderly people, some

with oxygen tanks, stood in long lines in the cold, waiting for the vaccine.

Others crowded clinics and doctors' offices, increasing their chance of

exposure to flu and other infectious agents.

With uncertainties about this year's vaccine supply, the CDC again

recommended that highest-risk people get priority for flu shots, at least

until late October. But last year's flu season may have left people confused

about essential points: Just how risky is the flu? And just how effective is

the vaccine? The answers to these questions may surprise readers.

How Risky Is the Flu?

First, a caveat: The risk calculations we analyze here describe typical flu

seasons only. We don't consider here what the picture would be in the event

of a deadly flu pandemic -- a worldwide outbreak of a new, highly virulent

flu strain, the potential for which has recently drawn considerable media

attention. No one really knows how likely such an outbreak is, but the risk

profile would certainly change. A pandemic is a fundamentally different

situation: The risk of death would be substantially higher, and untested

strategies (including new treatments, quarantine and a new vaccine) would

need to be implemented rapidly.

We deal here with what is known about typical flu seasons, based on data

that form the basis for the federal government's flu-risk figures.

By choosing to highlight the annual number of flu deaths, the CDC employed

an attention-grabbing tactic often used by public health and disease

advocacy groups. It's a tactic readers should be inoculated against if they

want a clear picture of the risks they face. (See " Research Basics:

Understanding How Big a Risk Is, " right.)

In fact, it is very difficult to know how many people die from any given

disease because there is often much uncertainty in determining the cause of

death. This is particularly true for the flu. That's because it shares

symptoms with so many other diseases, and because people most likely to die

a flu-related death are also at high risk for many other causes of death.

Flu deaths are probably undercounted because doctors do not routinely test

for the flu, and because some deaths that should be attributed to the flu

are given other diagnoses. For example, someone who dies from a heart attack

because they are debilitated by the flu might not get counted as a flu

death. Some overcounting of flu deaths also occurs: Clearly not all winter

pneumonia deaths are caused by the flu.

According to the CDC, 90 percent of flu-related deaths occur among people

age 65 years and older. Based on this information and the age distribution

of the population, the chance of a flu-related death for people in that age

group is about one in 1,000. Another way of saying this is that the chance

of not dying from flu for those 65 and older is about 999 out of 1,000. (For

context, the chance of a flu-related death is slightly lower than the chance

of dying from a fall or other accident.)

For people younger than 65 (including children), the chance of a flu-related

death is much smaller -- about one in 100,000. Of course, adults and

children might be concerned about flu-related problems besides death, such

as being hospitalized or just suffering with unpleasant symptoms (typically

three to seven days of fever, muscle aches, headache, weakness, dry cough

and runny nose). As you might guess, counting the number of flu-related

hospitalizations or the number of people experiencing symptoms from the flu

is even more difficult than counting flu deaths.

How Good Is the Vaccine?

Getting a shot does not guarantee you will not get sick from the flu or die

from it. Recently, the Cochrane Collaboration, an international group that

evaluates the evidence for various medical interventions, reviewed the

medical literature on the effectiveness of the flu vaccine in preventing

death.

Unfortunately, the evidence on how well the vaccine works to prevent death

in the elderly is limited. Few of the existing studies are randomized

trials -- considered the gold standard for medical evidence. Instead, most

data are from observational studies -- studies in which scientists simply

count up outcomes (here, the number of deaths that occur among people who

did or did not get the vaccine).

But drawing conclusions about cause and effect from such observations is

fraught with problems.

For example, a 2003 study published in the New England Journal of Medicine

observed that the flu vaccine was associated with a 50 percent reduction in

the overall death rate (that is, death from heart disease, stroke, cancer

and all other causes combined). To attribute an effect of this magnitude

solely to the flu vaccine is ludicrous: Flu-related deaths make up less than

2 percent of all deaths. If the claim were accurate, the vaccine's power

would dwarf that of any other medical intervention. There is, however, a

much more likely explanation: People who choose to get a flu shot are much

healthier -- and therefore already at much lower risk of death -- than

people who do not.

Only five randomized trials have examined the effectiveness of the flu

vaccine. In these studies, patients were randomly assigned -- a selection

technique equivalent to the flip of a coin -- to get either a flu vaccine or

a placebo injection. But none of these studies looked at whether the vaccine

prevents death. Instead, the scientists measured who developed a flu-like

illness. For a summary of the findings of these studies, see " How Well Does

the Vaccine Work in the Elderly? " below.

In the absence of good randomized trial data, it is still possible to gauge

the effectiveness of vaccination by looking at time trends in flu vaccine

rates compared with flu-related deaths in the elderly. As more people get

vaccinated, you would expect the flu-related death rate to decline -- if the

vaccine is effective. But, as the graph below, titled " A Windening Gap, "

shows, despite a dramatic increase in vaccination among the elderly, deaths

from the flu and pneumonia have hardly budged. (The calculations have taken

into account the aging of the population.)

For younger adults, flu-related death is so rare that it has not been

reliably studied: Doing so would require a trial of millions of people.

Of course, the flu shot may have benefits besides reducing the chance of

death. Many may get flu shots simply to avoid getting sick. The Cochrane

Collaboration identified more than 20 randomized trials addressing this

question. The overall chance of developing " clinical " flu (we'll explain in

a minute) was 19 percent in those chosen, again by chance, to receive the

recommended flu vaccine vs. 23 percent in the control groups.

The careful reader may notice that these percentages are substantially

higher than those reported for the elderly. (See " How Well Does the Vaccine

Work in the Elderly? " ) This is because clinical flu is defined as a set of

non-specific symptoms including fever, cough and muscle aches -- symptoms

shared by many non-flu illnesses like the common cold. These non-flu

illnesses may be especially common in younger adults because of their

exposure to other people, particularly children. To try to isolate the

effect of the vaccine, scientists sometimes use laboratory tests to confirm

the activity of flu virus in the blood. Using this measure, the chance of

flu in the vaccine group is 2 percent vs. 7 percent in the control group.

Studies have also measured another outcome: how vaccination affects days

lost from work. On average, there are about 0.16 fewer days lost from work

per person vaccinated. Another way of saying this is that about 5 percent of

those vaccinated avoid missing about three days of work because of the flu.

(That is, 0.16 days divided by the 5 percent who benefited from vaccination

equals 3.2 days.) The other 95 percent vaccinated got no benefit.

Take-Home Messages

To promote vaccine use, many in the public health community have overstated

the risk of flu-related death and the effectiveness of the vaccine in

preventing it. While the flu vaccine may have some important benefit (less

flu-related illness), we really do not know whether it reduces the risk of

death. For younger individuals -- for whom the chance of flu-related death

is extremely small -- any death-protection benefit can only be very modest

(and it is unlikely we will ever reliably know whether it even exists).

However, we do know that the vaccine reduces the risk of being sick and time

lost from work. But because the effect is small, individuals will have to

judge for themselves whether it's worth the bother.

We are not suggesting that Americans forgo flu vaccines. We simply want to

help people make informed decisions.

For many people, getting the vaccine is a reasonable choice. And many may

reasonably choose not to get it. (Consequently, the use of flu vaccination

rates by Medicare and others to measure health care quality probably does

not make sense.)

Regardless, public health officials should not exaggerate risks or benefits

to promote vaccination. Exaggeration carries a price: Not only do some

people get scared and engage in behaviors that increase their risk (like

waiting in a crowded clinic for a flu shot). They may also grow cynical and

end up ignoring health messages that really matter.

Woloshin, Schwartz and Gilbert Welch are physician-researchers

in the VA Outcomes Group in White River Junction, Vt., and faculty members

at the Dartmouth Medical School. They conduct regular seminars on how to

interpret medical studies. (Seehttp://www.vaoutcomes.org.) The views

expressed do not necessarily represent the views of the Department of

Veterans Affairs or the United States Government.

To respond to this article, send e-mail to health@....

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