Posted on October 29, 2011 There are critical 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 researchers conducted an analysis of 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 authors found that trivalent inactivated vaccine, which is used for 90% of influenza vaccinations in the United States, is only effective in preventing infection in 59% of healthy adults. 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. Earlier research had shown vaccines to be from 70% to 90% effective in healthy adults if matched to the circulating strains. “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. Lancet Infect Dis. Published online October 25, 2011.