U.S. expresses concern about vaccine as flu cases up

[Guest guest]

By Will Dunham Fri Feb 8, 5:28 PM ET

WASHINGTON (Reuters) - 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 d)