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.