The overall effectiveness of the seasonal influenza vaccine against influenza A and influenza B virus infection is 48% thus far, CDC reports. The estimate is based on data from 3,144 children and adults enrolled in the U.S. Influenza Vaccine Effectiveness Network from November 28, 2016 to February 4, 2017. According to CDC, most influenza infections were caused by A(H3N2) viruses. The vaccine's effectiveness was estimated to be 43% against illness caused by influenza A(H3N2) virus and 73% against influenza B virus. The interim vaccine effectiveness estimates indicate that influenza vaccination lowered the risk for outpatient medical visits by nearly 50%. CDC and the Advisory Committee on Immunization Practices stress that because influenza activity remains elevated, annual influenza vaccination efforts should continue as long as influenza viruses are circulating. The report further notes that "influenza A (H3N2) viruses undergo more frequent and extensive genetic changes than do influenza A (H1N1) and influenza B viruses, and require more frequent updates to the A (H3N2) vaccine virus components to maintain activity against evolving circulating strains." In addition, the report points to "substantially lower" rates of influenza-related hospitalizations thus far in the 2016–17 influenza season.