Interim Adjusted Estimates of Seasonal Influenza Vaccine Effectiveness - United States, February 2013

The updated adjusted estimates based on 2,697 children and adults enrolled in the US Influenza Vaccine Effectiveness Network during Dec 3, 2012-Jan 19, 2013 is featured. During this period, overall vaccine effectiveness (VE) against influenza A and B virus infections associated with medically attended acute respiratory illness was 56%, similar to the earlier interim estimate. VE was estimated as 47% against influenza A virus infections and 67% against B virus infections. When stratified by age group, the point estimates for VE against influenza A and B infections were largely consistent across age groups, with the exception that lower VE against influenza A was observed among adults aged ≥65 years. These adjusted VE estimates indicate that vaccination with the 2012-13 influenza season vaccine reduced the risk for outpatient medical visits resulting from influenza by approximately one half to two thirds for most persons, although VE was lower and not statistically significant among older adults. A CDC editorial note is presented.