Figure 2.

Antibody responses to the influenza vaccine in young and older subjects. Serum samples obtained from 89 vaccine recipients before and ∼3 weeks after vaccination are assayed for HAI against each vaccine strain of the influenza virus to determine the antibody response to the vaccine. Seroconversion (⩾4-fold increase) is calculated and the number of strains that subjects seroconverted against is used to define response categories; seroconversion to 0 or 1 strain is considered as a poor response (PR), whereas seroconversion to 2 or all 3 strains is considered as a good response (GR) to the vaccine (A). (B) Percentage of PR and GR for young and older subjects. (C) Pre-vaccine geometric mean titer for all strains in young versus older subjects. **P-value <0.01.