Rubella specific cell-mediated and humoral immunity following vaccination in college students with low antibody titers.

OBJECTIVE: This study measured cell-mediated immunity (CMI) and antibodies to clarify the basis of rubella reinfection after vaccination. METHODS: In a pool of 65 college students, 39 who exhibited hemagglutination-inhibition (HI) antibody titers against rubella of ≤ 1:16 were vaccinated with a rubella vaccine. The CMI was assessed with interferon-gamma release assay. RESULTS: There was low correlation (r = 0.24) between the antibody titers and interferon-gamma levels at pre-vaccination status. Preexisting interferon-gamma levels were low in some subjects with low HI antibody titers of 1:8 and 1:16. Fifty-seven percent (4/7) of the subjects who were antibody-negative with past history of rubella vaccination at entry onto the study exhibited CMI. And 57% (4/7) of the subjects remained antibody-negative following a second vaccination, despite exhibiting CMI. HI antibody titers increased significantly after vaccination, whereas post-vaccination interferon-gamma levels did not exhibit significant increases. When subjects were divided (based on their past history of vaccination and antibody values) into natural infection and vaccination groups, HI antibody titers (mean ± SD) increased to 1:2(4.4 ± 1.4) from 1: 2(3.2 ± 0.4) (p = 0.065) in the natural infection group and to 1:2(4.4 ± 1.0) from 1:2(3.0 ± 0.8) (p < 0.00001) in the vaccination group following vaccination. The same classification revealed that interferon-gamma values did not increase significantly in either group following vaccination, but the interferon-gamma values at pre- and post-vaccination in the natural infection group were significantly higher than those at pre- and post-vaccination in the vaccination group (p < 0.05 and p < 0.05, respectively). CONCLUSION: Pre-vaccination interferon-gamma levels in each HI antibody titer group were similar. And there were some subjects with antibody-positive exhibited CMI-negative. These data may explain why rubella reinfection can occur in vaccinated seropositive individuals.