Flu Outbreak in a Vaccinated Closed Population — 2014

The efficacy of seasonal influenza vaccines varies from about 55% to 70% when the vaccines' influenza A components are well matched to the circulating viruses but may be far lower when they are not.

Over the course of 3 days in February 2014, 25 of 102 sailors aboard a moored U.S. Navy minesweeper sought medical care for influenza-like illness (ILI). Although rapid influenza testing indicated 16 cases of influenza A, polymerase chain reaction testing of nasal swabs identified 20 cases of this illness; the 18 specimens that could be subtyped were all H3N2. The hemagglutinin gene sequence of outbreak isolates were 99% identical to those of the strains circulating that season and were antigenically similar to the H3N2 component of the vaccine t…