Decreased antibody response among nursing home residents who received recalled influenza vaccine and results of revaccination, 1996–97

Abstract

In November 1996, 11 lots of one U.S. manufacturer’s 1996–97 trivalent influenza vaccine were voluntarily recalled because of decreasing potency of the A/Nanchang/933/95 (H3N2) component. Because the elderly are at high risk of developing influenza-related complications, we assessed the postvaccination antibody titers of nursing home residents who received recalled vaccine and assessed the antibody response to revaccination. Blood samples were collected 3 weeks after vaccination from 86 residents at three nursing homes who received recalled vaccine and 86 residents at three other nursing homes who received a different manufacturer’s vaccine. Medical records were reviewed. Residents of one nursing home were later revaccinated. Blood samples were collected on the day of revaccination and again in 3 weeks. Serum was tested by hemagglutination inhibition for antibody to all three components of the 1996–97 influenza vaccine. The geometric mean antibody titer (GMT) (33 vs 55; p=0.01) and the percentage of residents with an antibody titer ≥1:40 (52 vs 67%; p=0.04) to the A/Nanchang/933/95 component were lower among residents who received recalled vaccine compared to those who received non-recalled vaccine, but had similar GMTs against the other two vaccine components. After revaccination, the GMT to A/Nanchang/933/95 increased from 24 on the day of revaccination to 39 ( p=0.01) in residents from one nursing home. Therefore, vaccination with the recalled vaccine was associated with lower postvaccination antibody titers to A/Nanchang/933/95, but not against the other two vaccine components. Revaccination was moderately effective in increasing antibody titers. With annual changes in influenza vaccine strains, routine post-release stability testing of influenza vaccine should continue.