Influenza B vaccine strain selection continually problematic

The unpredictability of influenza B strains has complicated influenza vaccine strain selection every year and is one of the reasons the vaccine’s evolution has developed at a “glacial” pace, according to a speaker at the 14th International Congress on Infectious Diseases in Miami.

“Type B is a real problem,” Arnold S. Monto MD, professor of epidemiology at the University of Michigan School of Public Health in Ann Arbor, said at the meeting. “Recently there have been two lineages circulating: Victoria and Yamagata. You can’t predict which one is going to show up.”

Monto said that instead of trying to predict which influenza B strain will appear, it may be better to alternate the two strains in the vaccine. Another solution he suggested was to include a half dose of each: 7.5 mcg of the Victoria strain and 7.5 mcg of the Yamagata strain.

“The problem with these approaches is that they could raise complications,” Monto said. “We may have a hard time keeping people straight about the differences between the vaccines.”

Monto discussed influenza vaccination in specific populations, including children and the elderly. He cited data that indicated that 15- to 71-month-old children responded well to a live attenuated vaccine.

“They may have responded well to this vaccine because they do not have a lot of antibody production,” he said.

Efficacy rates in older populations continue to be the subject of debate, according to Monto. “The frailty issue is a big concern,” he said. “Many researchers believe that elderly vaccinated individuals are unhealthy to begin with, so they are more likely to get an influenza-like illness anyway. We are seeing outbreaks in nursing homes that have 80% to 90% coverage.”

Progressive changes in the immune systems of elderly individuals, known as immunosenescence, may lead to loss of functionality. Monto suggested that new approaches to influenza vaccination may be necessary.

“Seed virus in cells is one approach,” he said. “Vaccines that are not as dependent on precise strain selection is another. We should try to broaden the immune response to adjuvants. Production technologies need to increase for mammalian and nonmammalian cells. We have a ways to go with influenza vaccination.” – by Rob Volansky

For more information:

Monto AS. #11.002. Presented at: 14th International Congress on Infectious Diseases; March 9-12, 2010; Miami.

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