* Up to 579,000 deaths, not 18,500
* 51 percent of fatalities in Africa, southeast Asia
* Elderly accounted for just 20 percent of deaths
By Sharon Begley
NEW YORK, June 25 (Reuters) –
The swine flu pandemic of 2009 killed an estimated 284,500
people, some 15 times the number confirmed by laboratory tests
at the time, according to a new study by an international group
of scientists.
The study, published on Tuesday in the London-based journal
Lancet Infectious Diseases, said the toll might have been even
higher – as many as 579,000 people.
The original count, compiled by the World Health
Organization, put the number at 18,500.
Those were only the deaths confirmed by lab testing, which
the WHO itself warned was a gross underestimate because the
deaths of people without access to the health system go
uncounted, and because the virus is not always detectable after
a victim dies.
The new study also shows the pandemic’s impact varied widely
by region, with 51 percent of swine flu deaths occurring in
Africa and southeast Asia, which account for only 38 percent of
the world’s population.
“This pandemic really did take an enormous toll,” said Dr.
Fatimah Dawood of the U.S. Centers for Disease Control and
Prevention, who led the study. “Our results also suggest how
best to deploy resources. If a vaccine were to become available,
we need to make sure it reached the areas where the death toll
is likely to be highest.”
Swine flu, caused by the H1N1 influenza virus, infected its
first known victim in central Mexico in March 2009. By April it
had reached California, infecting a 10-year-old, and then
quickly spread around the world, triggering fears and even
panic.
The CDC warned Americans not to travel to Mexico if they
could avoid it. Egypt ordered the slaughter of all the country’s
pigs in a misguided attempt to contain the virus, which was in
fact spread from person to person.
The fears reflected the unusual nature of the virus, which
contained bits and pieces of bird, swine and human flu viruses,
a combination never before detected.
More Top Picks Treadmills
Scientists were unsure how transmissible or deadly this
mongrel flu would be, but early signs were ominous: the World
Health Organization declared swine flu a pandemic in June 2009,
when labs had identified cases in 74 countries.
Such lab-based identification is the gold standard, but
every expert acknowledges that it misses more cases than it
catches.
One reason is that “some people who contract flu do not have
access to health care,” said CDC’s Dawood, so their illness and
even death goes unnoticed by authorities. Another reason is that
the virus is not always detectable by the time a victim dies.
LACK OF DATA LOWBALLS FATALITIES
To get around these obstacles, epidemiologists resort to
statistical models. They typically take the number of deaths
from pneumonia and complications of underlying cardiovascular
disease – both caused by influenza – during non-flu periods,
count the number during a pandemic, and attribute the excess to
the flu.
Unfortunately, “vital statistics data are non-existent or
sparse in many lower-resource countries,” said Dawood, making
this approach infeasible.
Dawood and her colleagues – from Vietnam, Kenya, New
Zealand, Denmark and five other countries – tried a different
method.
They started with hard data, such as numbers from health
workers going door to door in rural villages and asking about
flu-like symptoms and testing nasal and throat swab samples, to
estimate the proportion of a country’s population infected with
2009 H1N1. Such data were available from 13 countries – wealthy,
such as Denmark, and poor, like Vietnam.
Then the scientists estimated the fraction of patients who
died in each country. They started with solid data on death
rates from respiratory illnesses in five wealthy nations.
Since someone with, say, pneumonia has a lower chance of
dying if treated in a top hospital in Hong Kong than at a rural
clinic in Vietnam, the scientists applied a “multiplier” to the
raw data from poor countries.
That is, they assumed that more people with flu-caused
pneumonia died in developing nations than developed ones.
These estimates and assumptions can introduce errors,
critics note. Newly released mortality data from Mexico, for
instance, show that H1N1 killed even more people than the new
study estimates, said Lone Simonsen of George Washington
University School of Public Health, co-author of a commentary on
the study. Estimates of deaths from Japan and Singapore, in
contrast, may be too high.
Overall, however, the under- and over-estimates probably
even out, said Simonsen, making the global estimate – of 15
times more deaths than those confirmed at the time – about
right.
More Top Picks Blueair Invisiblemist H35i
The results paint a picture of a flu virus that did not
treat all victims equally.
It killed two to three times as many of its victims in
Africa as elsewhere. Overall, the virus infected children most
(4 percent to 33 percent), adults moderately (0 to 22 percent of
those 18 to 64) and the elderly hardly at all (0 to 4 percent).
Even though the elderly were more likely to die once
infected, so few caught the virus that 80 percent of swine flu
deaths were of people younger than 65.
In contrast, the elderly account for roughly 80 percent to
90 percent of deaths from seasonal influenza outbreaks. They
were probably spared the worst of 2009 H1N1 because the virus
resembled one that had circulated before 1957, meaning people
alive then had developed some antibodies to it.
The relative youth of the victims meant that H1N1 stole more
than three times as many years of life than typical seasonal
flu: 9.7 million years of life lost compared to 2.8 million if
it had targeted the elderly as seasonal flu does.
H1N1 had begun petering out by November 2009, and the WHO
declared the epidemic at an end the following August.
(Reporting by Sharon Begley; Editing by Michele Gershberg and
Xavier Briand)