But it’s a study way back in 1999 that actually offers a possible explanation for these counterintuitive findings: “the antigenic distance hypothesis.” That is, the more different a particular vaccine’s strains are from the previous year, the more effective the vaccine is likely to be (assuming the vaccine strains match the circulating strains that year). But vaccine strains that are more similar to the previous year’s vaccine strains — such as last year’s H3N2 A strain, identical to the strain in the 2013-2014 season’s vaccine — may end up less effective, and we did see very low effectiveness last year because of the H3N2 strain.
No safe blood lead level in children has been identified. Lead exposure can affect nearly every system in the body. Because lead exposure often occurs with no obvious symptoms, it frequently goes unrecognized. CDC’s Childhood Lead Poisoning Prevention Program is committed to the Healthy People 2020 goals of eliminating blood lead levels ≥ 10 µg/dL and differences in average risk based on race and social class as public health concerns. The program is part of the National Center for Environmental Health's Division of Emergency and Environmental Health Services .