Influenza Vaccine May Not Protect As Well As Expected
- From: rpautrey2 <rpautrey2@xxxxxxxxx>
- Date: Sat, 9 Feb 2008 10:33:02 -0800 (PST)
U.S. expresses concern about vaccine as flu cases up
By Will Dunham
Fri Feb 8, 5:28 PM ET
The influenza vaccine given to Americans may not protect as well as
expected, U.S. health officials said on Friday as the number of flu
cases increased nationwide.
The U.S. Centers for Disease Control and Prevention said slightly more
than half of the influenza virus strains reported to its surveillance
system are not good matches against the strains included in this flu
season's vaccine.
The number of states reporting widespread flu activity jumped to 31
this week compared with 11 a week ago, the CDC said. But Dr. Joe
Bresee of the CDC's influenza division said there are no indications
this flu season is worse than usual.
"Seasonal flu activity was slow to start this year but has increased
sharply in recent weeks," Bresee told reporters.
One measure officials use to gauge the severity of the season is the
number of flu-related child deaths. Bresee said the CDC has heard of
six U.S. children who have died from the flu, a relatively low number
compared with recent years.
Flu viruses mutate and change all the time, so every year a different
vaccine is created as officials predict which particular strains will
circulate.
The vaccine is designed to protect against three influenza strains --
two from Type A, an H1N1 and an H3N2 version, and one for Type B.
Bresee said about 30 percent of the overall strains of influenza in
the United States may be a Type A strain that emerged in Australia
called H3N2 A/Brisbane. It emerged too late to be included in the flu
vaccine offered in the United States beginning in September and
October.
The Type B strain chosen for this year's vaccine also was not a good
match for most of the B virus strains seen in the United States this
flu season, Bresee said.
"While a less-than-ideal virus match between the viruses in the
vaccine and those circulating viruses can reduce vaccine
effectiveness, we know from past influenza studies that the vaccine
can still protect enough to make illness milder or prevent flu-related
complications," Bresee said.
Bresee noted that decisions on the composition of the annual vaccine
are made about nine months before it is made available to the public
in the fall, and it is sometimes hard to know that far in advance
which strains will circulate.
Flu vaccines take months to make.
Bresee also said some resistance is being reported to the antiviral
drug Tamiflu, made by Switzerland's Roche Holding AG and Gilead
Sciences Inc of the United States. Of the viruses tested in CDC flu
labs, 4.5 percent are resistant to the drug, Bresee said.
Influenza kills an estimated 36,000 Americans in an average year, and
puts 200,000 into the hospital, the CDC said.
(Editing by Maggie Fox and Xavier Briand)
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