Effectiveness of present flu vaccines may not be satisfactory: Study

By Dr. Ananya Mandal, MDOct 26 2011

According to a report published online October 25 in The Lancet Infectious Diseases there are gaps in the evidence for the effectiveness of licensed influenza vaccines in the United States. Individuals who are at risk for medical complications or people who are aged 65 years or older are especially affected by the gaps, the researchers write.

The report is a compilation of results from 31 studies that used laboratory tests to confirm influenza infections. These studies were selected from 5707 studies identified, published over a period of 40 years.

The trivalent flu shot, which is the one offered at most doctors’ offices and pharmacies, reduced the risk of illness 59 percent of the time, according to the review of 10 studies that spanned 12 flu seasons. The vaccine is designed to guard against the three most popular flu strains each season, which in 2012 include H1N1, H3N2 and influenza B.

They also found live attenuated influenza vaccine, which is not approved for adults who are aged 50 years or older, to be effective in 83% of children aged 7 years or younger, and in 69% of people younger than 65 years.

“The ongoing health burden caused by seasonal influenza and the potential global effect of a severe pandemic suggests an urgent need for a new generation of more highly effective and cross-protective vaccines that can be manufactured rapidly,” write Michael Osterholm, from the University of Minnesota, Minneapolis, and lead author of the study, and colleagues. “In the meantime, we should maintain public support for present vaccines that are the best intervention available for seasonal influenza.”

The researchers noted that there were actually no published papers on randomized controlled trials of trivalent inactivated vaccine efficacy in people aged 2 to 17 years or in adults aged 65 years and older. They also found no such trials for live attenuated influenza vaccine efficacy in people aged 8 to 59 years. In addition, they found “substantial variability” by season and age group.

“The difference between 69% effectiveness and 90% effectiveness (or greater) will have a major public health effect in any pandemic that causes serious morbidity or increased mortality,” the researchers write. They recommend that industry and government form partnerships to accelerate research and reduce regulatory barriers to bring new vaccines already in development to market.

The ever-evolving flu virus complicates the development of vaccines, which are strain-specific. “That’s why we need a new vaccine every year,” said Dr. William Schaffner, chairman of preventive medicine at Vanderbilt University Medical Center. But scientists are working toward  a stronger, more universal vaccine that could be a one-shot deal — with the occasional booster.

In a commentary also published in Lancet Infectious Diseases, Heath Kelly at  the Victorian Infectious Diseases Reference Laboratory in Melbourne, Australia, and Marta Valenciano at EpiConcept in Paris, argue those estimates should be revisited. “Now might also be an appropriate time to use revised estimates of the most probable effectiveness of influenza vaccines to re-examine the effectiveness and cost-effectiveness of some policy options,” they wrote.

The U.S. Centers for Disease Control and Prevention recommends that anyone older than 6 months get a flu shot every year. But only one-third of eligible American’s got vaccinated last year. “There’s still time to get vaccinated,” said Schaffner. “It’s widely available and absolutely everybody should go out and get it.”