Flu Outbreak Aboard Navy Ship Highlights Possibility of Illness in Vaccinated Populations

By Amy Orciari Herman

Edited by André Sofair, MD, MPH, and William E. Chavey, MD, MS

An outbreak of influenza A (H3N2) among a largely vaccinated Navy crew in February 2014 demonstrates the flu risk that remains among vaccinated populations. The outbreak is described in MMWR.

In February 2014, 25 otherwise healthy Navy crew members aboard a ship moored in California developed influenza-like illness. Polymerase chain reaction testing of nasal specimens confirmed influenza A in 20; of these, 18 were subtype H3N2, and 2 could not be subtyped. The virus was antigenically similar to the H3N2 component of the 2013-2014 vaccine, and 17 of the 18 with confirmed H3N2 had been vaccinated at least 3 months earlier (overall, 99% of the crew had been vaccinated).

Symptomatic crew members were given oseltamivir and sent off the ship for 48 hours. Other infection-control procedures, including thorough cleaning of the ship, were followed. No other cases were reported.

"Despite vaccination measures, influenza outbreaks can still occur in highly vaccinated ... populations," MMWR's editors conclude.