Antibody response to a sub-potent influenza vaccine among nursing home residents and results of revaccination, New York, 1996-97

Abstract

Background: In November 1996,11 lots of 1996-97 trivalent influenza vaccine were recalled because of decreasing potency of the A/Nanchang/933/95 (H3N2) component. Since higher antibody liters afford greater protection against influenza and because elderly persons are at high risk of influenza-related complications, we assessed the antibody titers of nursing home residents who received either recalled vaccine (RV) or non-RV. We then assessed the antibody response to revaccination among a subgroup of residents who had first received RV. Methods: We studied 86 residents from 3 nursing homes who received RV and 86 from 3 other nursing homes who received non-RV. Medical records were reviewed and blood samples were obtained 3 weeks after vaccination. Serum was tested by hemagglutination inhibition (HI) for antibody to all 3 components of the 1996-97 influenza vaccine. Sera collected from 23 residents from one nursing home before and 3 weeks after revaccination with normal potency vaccine were also tested by HI. Results: The geometric mean antibody titer (GMT) (33 vs. 55; p =0.01) and the percentage of residents with an antibody tiler >1:40 (52% vs. 67%; p = 0.04) to the A/Nanchang component were lower among residents who received RV than among residents who received non-RV. In the 23 residents assessed for response to revaccination, GMT to the A/Nanchang component increased from 24 to 39 (p=0.01) after revaccination. Conclusions: Residents who received RV had lower post-vaccination antibody titers to A/Nanchang than did those who received non-RV. Revaccination of residents who first received RV was associated with a rise in titer to the A/Nanchang component.