WSJ: How Deadly Is Bird Flu? It Depends

[Guest guest]

THE NUMBERS GUY By CARL BIALIK

Just How Deadly Is Bird Flu? It Depends on Whom You Ask

January 13, 2005

This is the first installment of The Numbers Guy, a new column on the

way numbers and statistics are used – and abused – in the news,

business and politics.

The World Health Organization has a big problem: It needs to alert

the public to the dangers of a virus that has killed very few people,

yet could, in some scenarios, devastate nations across the globe.

So, the group's doctors and scientists have lately been forecasting

truly alarming numbers from the so-called Asian bird flu -- up to 100

million deaths. One researcher has gone much further, suggesting the

toll could be up to a billion people.

But projecting death counts from such a bug isn't just an inexact

science; it's more like educated guesswork. The truth is, scientists

don't know the rates at which this hypothetical flu -- derived from a

bird flu that so far in Asia doesn't spread well from human to human -

- could infect and kill. They base guesses on prior flu pandemics,

but there's no way to quantify how much better we're prepared in

2005, thanks to improved vaccine production and antiviral medication,

than we were in 1968, when the last flu pandemic struck.

Some numbers are flat-out wrong, misleading or biased. Others are

valid and useful, helping us to make informed decisions. As The

Numbers Guy, I will try to sort through which numbers to trust,

question or discard altogether. And I'd like to hear from you at

numbersguy@.... I'll post and respond to your letters.

Read comments from readers on this column.Then again, the next

pandemic could be worse than that relatively mild one, and even worse

than the deadliest of the past century, in 1918, which killed at

least 20 million people at a time when the world had a smaller

population which traveled less.

The most responsible answer, then, to the question of how many people

the flu will kill is, " We don't know. " But big numbers get headlines

while honest uncertainty usually doesn't. And the WHO has been

sharing big numbers, like two million to seven million people dead

world-wide. At a press conference in Hong Kong two months ago, one

official went further, saying this hypothetical pandemic could kill

as many as 100 million people. The WHO always cautions that these

aren't sure numbers, but the group shouldn't be surprised that the

press often skips the complexity.

The 100 million figure was reported widely, including in the New York

Times, The Wall Street Journal Online, CNN, Newsweek and the U.K.'s

Observer; but without much caution about how arbitrary it is.

At issue is H5N1, a new strain of bird flu that so far has killed a

few dozen people in Asia -- nearly three quarters of the number of

people known to have been infected. Scientists fear the virus will

spontaneously mutate or swap parts of its genetic code with another

virus, and thereby become more transmissible. They hope that in doing

so, it also will become less lethal. But there is no way to know.

(Dutch researchers recently found that a different strain of bird flu

had spread widely among humans in 2003, but killed few of those

infected.)

Henry Niman, who studies viruses and criticizes the WHO for being

underprepared, says that in the true worst-case scenario, one billion

people could die. That figure was reported in the New York Times. Dr.

Niman's reasoning: The current mortality rate among those known to

have been infected is nearly 75% and the WHO is estimating that one

billion to two billion could be infected world-wide. But Dr. Niman, a

medical researcher in Pittsburgh whose company, Recombinomics Inc.

seeks to develop vaccines for viruses, adds, " There are a lot of

variables. The concept that you can't really put a number on [the

estimated death toll] at this time, is certainly valid. "

This all matters a great deal to companies deciding whether to

develop a flu vaccine, to hospitals making worst-case plans, to

scientists seeking research grants and even to public citizens who

have never heard of bird flu. Steep death-toll projections are very

powerful numbers that can drive action. If the numbers are accurate

and shared responsibly, they are a force for public good. If they are

misleading or hide uncertainty, they can lead to wasted resources and

poor decisions.

Meltzer, a senior health economist with the office of

surveillance in the National Center for Infectious Diseases at the

Centers for Disease Control and Prevention in Atlanta, who made the

calculations for the WHO, based his model on the 1968 flu pandemic

for a 1999 paper estimating the potential death toll in the U.S. (The

model is outlined in an online appendix.)

Here's how Dr. Meltzer and his colleagues arrived at the upper

estimate of seven million dead: They estimated the rate of infection

in the U.S. could be between 15% and 35% (in somewhat circular

logic, they chose a minimum of 15% simply because anything lower

wouldn't be much of a pandemic). Then they assigned the expected

cases to three age groups, based on U.S. Census data and two models

of how infection rates would distribute among age groups, based on

prior flu pandemics. (In one model, more people under 20 are

infected). Next they used estimates from prior studies to calculate

those members of each age group who were at high risk of suffering

adverse effects from the flu -- generally people with certain pre-

existing medical conditions.

To calculate deaths, they used rates from the 1968 flu pandemic. They

used different death rates for different age groups and number of

risk factors, based on a study of outcomes for Oregon patients who

contracted the prior flu. The estimate for deaths in the U.S. ranged

from 89,000 to 207,000, depending on the rate of infection. Then last

year Dr. Meltzer, in an unpublished calculation for the WHO,

extrapolated the U.S. numbers to the world, using estimates of

population, age range and risk factors.

Of course, there is plenty of uncertainty in this model. The

distribution of risk factors is not known, for instance, in many

parts of the world. And the effects of different risk factors on

likelihood of death also are unclear. Just one example of the

guesswork involved: " Data regarding the death rate among 0-19 years

old with high risk conditions are scarce. " So the authors use a model

of how pneumonia death rates among people age 44 and under are

affected by risk factors -- a different disease and different age

group. Also, historical numbers may be the best ones we have, but

they come from a different virus, a different era and a different

medical system. (Then there's the question of how we know exactly how

many died in prior pandemics; perhaps that's a topic for a future

column.)

These calculations aren't driven by any specific aspect of H5N1, but

that virus's lethality is fueling a growing fear that we are due for

a pandemic. Historically, we have had three or four each century, yet

the last one to strike came in 1968. But this is essentially the

gambler's fallacy of assuming that 10 straight bad bets mean a

winning wager is imminent.

The research itself isn't at fault; striving to make estimates based

on imperfect data is typical in science. What's questionable is the

way the estimates have been used by public-health officials.

Dr. Meltzer acknowledges that his initial paper was based on many

assumptions, and calls the extrapolation of U.S. numbers to the

world " rough estimates. " He urges people to create their own numbers

by plugging different starting figures for things like infection rate

and mortality into his online software (here): " My estimates may not

be correct, but the public should understand the quality of the

estimates. " Klaus Stohr, a WHO flu virologist, adds, " There are a

large variety of different models, all equally right and equally

wrong. "

Nonetheless, both men defend the WHO's decision to share numbers. " We

have come up with this information because we feel it is important to

share with the world, " Dr. Stohr says. " There are a number of

decisions governments and regional authorities can take that can have

an impact on pandemic preparedness. "

Dr. Meltzer points out that, beyond death tolls, his study also

estimated that hundreds of millions could become ill, which could

overwhelm hospitals. Thus it's important to prepare the public for

rationing and triage, and spark debate about how to allocate scarce

resources, should a pandemic strike. " One can cry wolf too many

times, " Dr. Meltzer says. " This isn't it. I don't think we've cried

wolf enough about pandemic flu. The problem is, how do you sustain

interest? "

But a faulty number can be worse than no number, especially when it

can evoke fear in the general population without advising any evasive

actions people can take. Schabas, Ontario's former chief

medical officer, contrasts influenza warnings with those about

tobacco. " Scaring people about avian influenza accomplishes nothing,

because we're not asking people to do anything about it. I don't see

the point of that, " says Dr. Schabas, now chief of staff at York

Central Hospital in Richmond Hill, Ontario, who wrote a column in the

Globe and Mail early last year criticizing bird-flu warnings.

Striking the right balance of fear is a delicate public-relations

art. In October 2003, New York University clinical associate

professor of medicine Marc Siegel thought more fear about the flu

would be a good thing. He wrote in a USA Today column, " To contain

it, we need more vaccinations, more isolation of those who are sick,

more hand washing -- and even, for once, a little more fear. "

But since then, thanks to numerous WHO warnings and the scare about

vaccine shortages for the more-common strain of flu this winter, Dr.

Siegel thinks the balance has shifted. " Flu has now become the

opposite of what it was then, " he says. " Now we probably have too

much fear of the flu. "

Dr. Meltzer's desire for robust public examination of his numbers,

and debate about public health is admirable. But realistically, since

neither public funds and people's attention are infinite, too much

fear about the flu can distract from other, less-novel but more-

dangerous diseases.

Lee Reichman, executive director of the New Jersey Medical School's

National Tuberculosis Center in Newark, shows a slide at seminars

comparing deaths world-wide in 2003 due to TB (between two and three

million annually) to those due to SARS, Ebola, the West Nile virus

and other highly publicized diseases -- a total of just barely 1,000.

Now he says he may add bird flu to the slide. " Someone in the U.S. is

far more likely to die of TB than of bird flu, " says Dr.

Reichman. " But there's a perception: [Tuberculosis] an old disease.

It's under control. "

Here are some of your letters to my column on bird flu. Letters have

been edited for space and clarity.

* * *

Silbert: I'm sorry you chose Asian bird flu as the topic for

your first column, here's why.

I agree the numbers are impossible to estimate with any real

accuracy. I also agree that the public can't protect themselves. Then

why are thoughtful, seasoned doctors like Fauci [of the NIH's

National Institute of Allergy and Infectious Diseases] speaking out

so strongly? I have never seen warnings like this coming from the WHO

or so many highly respected virologists around the world.

The reason isn't to scare the public. It's to alert governments to

use the time available wisely. Private warnings have had little

effect. There is no vaccine, and developing one is difficult, because

the present method of growing it in chicken eggs won't work. Bird flu

kills chicken embryos like it kills chickens… There are times when

arguing about the accuracy of numbers should take a back-seat to what

Dr. Fauci calls " the big picture. " I hope and pray somehow there is

nothing to worry about, but there is something relentless about this

virus that too many well-trained minds find very frightening indeed.

I wish you all the best with your new column. I also wish you hadn't

used your first opportunity on this superb bully pulpit to turn down

the heat on public officials to protect a public that can't protect

itself.

Carl: , thanks for the astute comments. The big picture about

avian flu is, indeed, frightening and deserves attention. But the WHO

would do far better to base its warnings to the public on the scary

numbers it does know with some certainty -- like the high death rate

among people infected with the Asian strain of avian flu, and the

death toll from prior flu pandemics. Speculative projections only

lessen the organization's credibility, and could make people

skeptical of other numbers that deserve more trust. The press is

complicit in demanding numbers and then often reporting them without

proper context. But it's still possible to gain public attention for

a serious danger without questionable numbers...

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