he influenza vaccine now being given was not developed
to protect against a strain of the virus that has surfaced in this country
this fall, but the government is optimistic that this year's vaccine will
stave off outbreaks, a top federal health official said yesterday.
The reason is that animal studies suggest that the strains of virus
included in the vaccine are close enough to the new one that the vaccine
will still protect, said the official, Dr. Julie L. Gerberding, the
director of the Centers for Disease Control and Prevention in Atlanta.
Still, she warned, the United States could face a severe epidemic this
year, given that the flu season began unusually early and has hit Texas
and Colorado particularly hard.
"It's a little too early to say whether or not this portends the worst
flu season we have had in a long time," Dr. Gerberding said in a telephone
news conference. Her agency is responsible for tracking and controlling
influenza and other infectious diseases.
She said she was "sounding the alarm" to urge more people to get flu
shots to "nip this problem in the bud." The center does not know how many
people have received flu shots this season. "People have the impression we
are doing better this year than last year, but we do not have the data to
back that up at this point in time," she said.
The flu vaccine includes three strains of influenza virus, but was not
designed to protect against a new one that has appeared in a number of
countries over the last year. It is known as the Fujian strain, a variant
of the Panama strain that is included in the current vaccine. Both are
categorized as H3N2 strains that have been linked to higher rates of
serious illness requiring admission to a hospital and to death, Dr.
Gerberding said.
Each year, influenza causes 114,000 hospital admissions and 36,000
deaths.
The influenza virus mutates frequently. Health officials change the
strains of virus put in the flu vaccine each year as they try to keep up
with mutations. But matching strains in the vaccine with those circulating
among humans during a flu season is a notoriously unpredictable
exercise.
The World Health Organization committee that makes the recommendations
for the flu vaccine knew about the Fujian strain in February, said Dr.
Klaus St�hr, an influenza expert at the organization. But Dr. St�hr said
in a recent interview that the committee decided not to include the Fujian
strain because scientists could not make it pure enough in time for a
human vaccine.
The flu vaccine is prepared in eggs. Decisions about the components of
the vaccine have to be made months in advance in part because
manufacturers and farmers need to know how many eggs to prepare in
anticipation of demand.
Influenza typically occurs during the winter in each hemisphere, and
the vaccines are prepared at different times. The vaccine being prepared
for use in the Southern Hemisphere will include the Fujian strain, Dr.
St�hr said.
"There may be less than optimal protection against H3N2" in the
Northern Hemisphere, "but no vaccine failure has been reported" there, he
said. "So there is no reason to discourage people from getting
vaccinated."
Dr. Gerberding said it was common for the circulating influenza to
gradually change genetically � known as "drift" � as it spread to infect
more people.
Tests at the center found that 84 percent of the 55 strains of
influenza virus isolated this fall are the Fujian strain, Dr. Gerberding
said. But she emphasized that protection could still occur even without a
perfect match.
Dr. Gerberding said that an earlier than usual onset of the flu had
occurred in some European countries but that "this is not a
pandemic."
