THURSDAY, Feb. 21 (HealthDay News) -- A U.S. Food and Drug Administration panel on Thursday approved the inclusion of three new flu strains in next year's batch of flu vaccine, in an unusual move that health officials hope will avoid the shortcomings of this year's vaccine.

Typically, only one or two strains are changed each year, and flu vaccine manufacturers need a long lead time, about eight months, to complete the entire production process for the 100 million doses due by the fall.

"We have things in the pipeline, but we are not in a situation we'd like to be this time of year with working seeds ready to go," Tony Colegate, of Novartis Vaccines and Diagnostics, told the FDA panel, according to Dow Jones Newswire. "We think this will be a very, very difficult year."

The expansion of flu strains for next year comes during a current flu season that has not been easy so far.

This year's flu shot has missed its mark badly, and the end result has been widespread or regional flu activity in virtually every state. Many of the infections are being caused by strains not covered by this year's vaccine, U.S. health officials have said. And some strains are becoming resistant to a common antiviral medication.

The U.S. Centers for Disease Control and Prevention first reported last week that this year's flu vaccine doesn't match two of the three strains of influenza currently circulating in the United States.

"Clearly, there is influenza going around in a lot of states," said Dr. Peter C. Welch, an infectious diseases expert at Northern Westchester Hospital in Mt. Kisco, N.Y. "Part of the issue is that the vaccine which was produced this year is not the most effective vaccine that we've had for influenza."

Because the influenza virus constantly changes structure, the vaccine must be reformulated every year. The World Health Organization announced last week its recommendations for next year's flu vaccine, which includes protection against the H3N2 strain and other strains not in this year's vaccine.

And the FDA panel on Thursday followed the WHO lead. The new flu strains include Brisbane/10, a version of the H3N2 flu; a second new Type A strain known as H1N1/Brisbane/59, and a newer Type B/Florida strain.

The virus strain most common in the United States right now is the influenza A H3N2 strain, and it's a strain not included in this year's vaccine. Also, this year's vaccine is not well-matched against influenza type B.

Complicating matters, some of this year's influenza type A virus is showing resistance to the antiviral drug Tamiflu. Overall, 8.1 percent of the influenza type A viruses tested by the CDC were resistant to Tamiflu. In past years, less than 1 percent of the viruses have been resistant to the drug.

The composition of a flu vaccine is not an easy prediction at best, Welch said.

"Although these are educated guesses, they clearly are guesses," he added. "Sometimes, they guess right. Sometimes, they guess wrong. This year, they didn't guess well. Sixteen out of the last 19 years they have guessed pretty well."

For the week ending Feb. 9, widespread flu activity was reported by 44 states and regional activity was reported by five, for a total of 49, according to the CDC's latest tally. During the three most recent flu seasons, the number of states reporting regional or widespread activity peaked at 41 to 48 states.

Ten children, ranging in age from 4 months to 14 years, have died from influenza so far this year, the CDC also reported. During the last three years, flu-related deaths among children have ranged from 46 to 74.

Even though this year's vaccine isn't a good match for most of the circulating flu virus, CDC officials continue to recommend that people get inoculated. The reason: The vaccine still offers partial protection and can reduce the risk of flu-related complications.

An estimated 5 percent to 20 percent of the U.S. population suffers from the flu each year. More than 200,000 people are hospitalized from flu complications, and about 36,000 people die from the disease. Some people, such as older individuals, young children, and people with certain health conditions (such as asthma, diabetes or heart disease), are at high risk for serious flu complications, according to the CDC.

More information

The U.S. Centers for Disease Control and Prevention has more on the flu and the flu vaccine.

SOURCES: Peter C. Welch, M.D., infectious disease expert, Northern Westchester Hospital, Mt. Kisco, N.Y.; Dow Jones Newswire; Feb. 22, 2008, Morbidity and Mortality Weekly Report, U.S. Centers for Disease Control and Prevention

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