UPDATE 1-In U.S., flu vaccine worked in just over half of those who got it

* Protection even lower among people 65 and older

* Officials say findings underscore need for better vaccines

By Julie Steenhuysen

CHICAGO, Feb 21 (Reuters) - A U.S. government analysis ofthis season's flu vaccine suggests it was effective in only 56percent of people who got the shot, and it largely failed toprotect the elderly against an especially deadly straincirculating during flu season.

The U.S. Centers for Disease Control and Prevention said thefindings underscore the need for more effective weapons in thefight against influenza, which kills between 3,000 and 50,000people in the United States each year depending on the severityof the flu season.

"We simply need a better vaccine against influenza, one thatworks better and lasts longer," CDC Director Dr. Thomas Friedensaid in a statement on Thursday.

Experts generally estimate the effectiveness of flu vaccinesto be between 50 percent and 70 percent, but this vaccineappears to have fallen on the low side of that range.

The vaccine did cut the risk of medical visits caused byeither influenza A or influenza B by 56 percent, according tothe study published in the CDC's Morbidity and Mortality WeeklyReport.

It was more effective against influenza B, protecting 67percent of those who were vaccinated. Against the influenza A(H3N2) strain, the vaccine protected only 47 percent.

The protective benefits of the vaccine against influenza Bwere consistent across age groups. That was not the case withthe influenza A (H3N2) component of the vaccine, which protected46 percent to 58 percent of people aged 6 months to 64 years,but only 9 percent of those 65 and older, a finding that wasstatistically insignificant.

The estimates are based on studies of 2,697 children andadults enrolled in the U.S. Influenza Vaccine EffectivenessNetwork between Dec. 3 and Jan. 19. The CDC said those estimatesmay change by the end of the flu season, when more people havebeen sampled.

Even so, the findings suggest that a large group of elderlypeople, who are consistently the most vulnerable to influenza, were unprotected during this year's flu season.

POOR IMMUNE RESPONSE TO VACCINES

One possible explanation may be that in older individuals,the immune system often produces a less robust immune responseto vaccines, or to any infection.

CDC experts suggested that poor immune response to theinfluenza A (H3N2) component of the vaccine may help explain whythe elderly were not protected, but said in the report thefindings "should not discourage future vaccination by personsaged 65 years (or older), who are at greater risk for moresevere cases and complications from influenza."

Dr. Joseph Bresee, a flu expert at the CDC, said overall thevaccine worked "OK," but it is not fully clear why people over65 responded poorly.

"Part of it is they are elderly and they respond lessvigorously to vaccines. But it appears that some of the people,at least, developed a less robust response to this particularantigen," he said, referring to the H3N2 component of the fluvaccine.

"Why that is, I don't think we know yet. We're looking at itclosely," he said.

Bresee said most of the elderly in the study tookconventional flu vaccine, and not the high-dose versiondeveloped by vaccine giant Sanofi to address issues ofpoor immune responses in the elderly.

"We'd love to be able to look at the question of whether itis actually more effective or not. We just don't have enough useyet," he said.

Sanofi said it shipped 6 million doses of the specialformulation for the elderly, but it did not have information onhow many of the doses were used, or whether any had been used bypatients in the study.

What is clear, Bresee said, is the need for the elderly whoget sick with flu symptoms to seek treatment with antiviralmedications, such as Roche Holding Ag's Tamiflu, whichcan reduce the severity of their illness.

CDC noted that vaccine effectiveness has been known to varybased on a number of factors including virus type, age, theparticular flu season and variations in an individual'simmunity.

"Although it's far from perfect, flu vaccination is by farthe best tool we have to protect from flu," Frieden said.

BETTER VACCINES

Frieden said the U.S. Department of Health and HumanServices as well as pharmaceutical companies are working toproduce better vaccines. Efforts include the use of geneticengineering to develop more potent and more modern flu vaccines,with the hope of ultimately developing a universal flu vaccinethat could protect against all strains of flu. Experts predictthat could be possible within eight to 10 years.

"It's going to be hard but it's well worth the effort,"Frieden said.

Already there are signs of change. In November, the Swissdrugmaker Novartis won U.S. Food and DrugAdministration approval for Flucelvax, a seasonal flu vaccinegrown in animal cell cultures instead of live chicken eggs, aspeedier and more reliable process that could help buildstockpiles in the event of a pandemic.

In December, GlaxoSmithKline won FDA approval for anew seasonal flu shot called Fluarix that protects against fourstrains of seasonal flu - known as a quadrivalent vaccine -instead of three strains, known as a trivalent vaccine. Theannouncement followed the approval last February ofAstraZeneca's four-strain flu nasal spray made by thecompany's MedImmune unit. Current vaccines tackled two A strainsand one B strain. The quadrivalent vaccines will add anadditional B strain.

Last month, the FDA approved the first gene-based fluvaccine developed by privately held Protein Sciences Corp, whichuses genetic engineering to grow portions of the virus in insectcells.

"What we're looking at is really incremental improvements,because if we could make the breakthrough improvements easily itwould have happened already," Dr. Leonard Friedland, vicepresident of clinical and medical affairs for vaccines in NorthAmerica at GlaxoSmithKline, said in an interview last month.

Glaxo's Fluarix is the first inactivated flu shot to includefour instead of three strains of flu.

"It was just licensed and will be available for nextseason," Friedland said, noting that Sanofi is also in theprocess of having their four-strain flu vaccine approved.

AstraZeneca's FluMist, a live, attenuated or weakened fluvaccine, will also have a four-strain version available for nextflu season.

Dr. Chris Ambrose, a vice president at AstraZeneca'sMedImmune unit, said the company plans to completely switch tothe four-strain version of Flumist.

Sanofi Spokeswoman Donna Cary said the company has producedflu vaccines for specific age groups, including its high dosevaccine for the elderly.

"The next step for the future is to get to the point wherewe don't need to develop a new vaccine every year," Cary said."The main thing we are all looking forward to is the universalvaccine."