The US Navy has a mandatory influenza vaccination policy, but even a high immunization rate couldn’t prevent a shipboard influenza outbreak in February 2014. Nearly one-quarter of the 102 crew members on a minesweeper moored in San Diego for 2 months developed symptoms attributed to influenza A(H3N2) virus, even though 99% of the affected men had been vaccinated.
The virus likely was transmitted from the surrounding San Diego community. All 25 crew members who developed influenza symptoms were otherwise healthy, and 24 had been vaccinated. Nasal swab tests confirmed that 20 sailors had contracted influenza A and 18 had subtype H3N2, which was antigenically similar to the H3N2 component of the 2013-2014 vaccine. Outbreaks can be especially virulent in a ship’s tight confines, with shared living and work spaces and ventilation systems that can easily circulate pathogens. (Aquino TL et al. MMWR Morb Mortal Wkly Rep. 2014;63:947-949).
Vaccinated Populations Can Get Flu. JAMA. 2014;312(24):2610. doi:10.1001/jama.2014.16349