finish line in just seconds, this pandemic
strain is “the guy running in Central
Park,” says microbiologist Peter Palese
of Mount Sinai Medical Center in New
York City.
The ways the virus is transmitted, how
easily it spreads through contact and
how long before symptoms show up are
the same as what experts estimate for
seasonal and other pandemic flus, says
epidemiologist Justin Lessler of Johns
Hopkins University in Baltimore, who
coauthored a report that appeared in the
Dec. 31 New England Journal of Medicine. “I don’t think there’s any evidence
that this virus is any different,” he says.
Lessler and his colleagues examined an
H1N1 outbreak in a New York City high
school. From that data, they estimate
that the virus moves through the population slightly less efficiently than some
previous seasonal influenzas. About
14 percent of people who came in contact
with an infected person ended up with
influenza symptoms. An infectee develops symptoms in about 1. 4 days, a length
of time similar to that of other influenzas,
the team also reports. And 2. 7 days elapse
between when an infector feels sick and
the newly infected feels sick, too.
Another study published in the same
Seasonal flu
Deaths
<1% 3% 93%
<1% 99%
souRCe: CdC, w. Thompson ET AL./in TeRna Tional CongRess seRies 2004
Age 0– 4 5–49 50–64 65+ Unknown
H1N1
unlike the seasonal flu, h1n1 targets the young. Though infection rates are hard to come by,
early indicators find that young people are more susceptible to infection than older folks. h1n1
hospitalization and death rates from april to june 2009 bear this out.
Seasonal flu
Hospitalizations
4%
Pandemic flu deaths in the U.S.
500,000
400,000
Number of deaths
200,000
300,000
The current flu is the
fourth to cause a
pandemic since the
beginning of the 20th
century. Though the
numbers are fuzzy,
the spanish flu of
1918 caused the
most deaths by far.
Asian ;u H2N2
Hong Kong ;u H3N2
100,000
Swine ;u H1N1
0
1918–
1957–
1968 –
2009
1919
1958
issue of the New England Journal examined household transmission rates and
found that the pandemic virus is less
likely to move from one person to another
than some of the viruses responsible for
past pandemics. Simon Cauchemez of
Imperial College London and colleagues
found that, on average, about 10 percent
of people living with a person infected
with H1N1 come down with the flu. For
seasonal flus, the same measure is anywhere from 10 to 40 percent.
A study in guinea pigs shows similar
results. The virus replicates and transmits in the animals at rates close to those
of a seasonal influenza strain, Palese and
colleagues report in the January Journal
of Virology.
The key to avoiding infection despite
exposure lies with virus-destroying antibodies. These tiny patrollers roam the
body on the lookout for harmful particles. When a threat is detected, the antibodies hitch on to the invader and call
in other immune system attack dogs to
prevent the virus from taking hold.
An inability of antibodies to recog-
nize H1N1’s proteins may explain one of
the most ominous pieces of news about
this virus: It seems to target young peo-
ple. The CDC estimates that from April
through December 12, 2009, about
50 million people under the age of 65
became infected, compared with about
5 million people over age 65.
