Annual influenza vaccination: immune response in patients over 10 years.

Objective: To determine the effect of repeated annual influenza immunization on the host's serum antibody.
Design: Ten year observational study with cohort design.
Setting: Cystic Fibrosis Center at St. Vincent's Hospital and Medical Center, New York City, NY.
Patients: Thirty-eight children and young adults with cystic fibrosis (CF).
Measurements: Serum hemagglutination inhibition (HI) antibody titers were determined at the time of vaccination and 4 weeks later each year in the fall before the influenza epidemic. Shwachman scores were determined each year.
Results: While the pre-vaccination and post-vaccination geometric mean serum HI antibody titers varied from year to year, no upward or downward trend was evident over the 10 year period. The reciprocal of the post-vaccination geometric mean HI titers ranged annually from 32 to 74 for the influenza A (H3N2) vaccine strains, from 53 to 133 for the influenza A (H1N1) strains, and from 18 to 174 for influenza B strains. In addition, the majority of vaccinees had a presumably protective post-vaccination serum HI titer > or = 1:40 each year for all three vaccine strains. The initial mean Shwachman score of the group was 77. The final score of 76 after 10 years was not significantly different.
Conclusions: Annual influenza vaccination appears to regularly induce presumably protective serum antibody levels in most CF children and young adults studied over a 10 year period.