Effectiveness of this season’s influenza vaccine

The Centers for Disease Control and Prevention has released early estimates of the effectiveness of this season’s influenza vaccine in preventing influenza infection. Influenza vaccine effectiveness is assessed each year by the U.S. Influenza Vaccine Effectiveness Network. Patients with acute respiratory infection (ARI) are enrolled in the study; respiratory samples are taken and the presence of influenza virus is determined by polymerase chain reaction. Data from 1,155 children and adults with ARI during December 3, 2012–January 2, 2013 were collected at five study sites and used to determine that the estimated vaccine effectiveness is 62% (95% confidence intervals = 51%–71%). This number represents the overall effectiveness of seasonal influenza vaccine for preventing laboratory-confirmed influenza virus infection associated with acute respiratory infection. Of 1,155 children and adults with ARI, 416 (36%) were positive for influenza A or B virus. Of these, 236 (57%) were influenza A virus (all H3N2) and 180 (43%) were influenza B viruses. The immunization rate for influenza cases was 32% and 56% for individuals who did not have influenza virus. The ARI of these patients was likely caused by another agent. It is known that this season’s influenza vaccine is a good match for the circulating viruses. Why then is vaccine effectiveness only 62%? Although the study does not distinguish between patients who received the inactivated (injected) or the infectious (...
Source: virology blog - Category: Virology Authors: Tags: Basic virology Information acute respiratory infection ARI flumist inactivated vaccine influenza intranasal vaccine LAIV viral virus Source Type: blogs