Restoration of varicella-zoster virus cell-mediated immune response after varicella booster vaccination

In older age groups, an increasing proportion of healthy adults with a positive varicella history have lost their capacity for a cell-mediated immune (CMI) response to varicella-zoster virus (VZV) antigen despite the presence of virus-specific humoral antibodies. While it remains a matter of speculation whether this decline is connected with a predisposition to herpes zoster, it is known that a second zoster attack is rare in immunocompetent individuals. In order to determine whether the VZV-specific CMI response can be restored through varicella vaccination, the immune status of a group with naturally occurring herpes zoster was compared with that of a group of vaccinated subjects. Twenty zoster patients were tested for VZV antibody and VZV-specific CMI within the first 4 days of the disease. Antibodies were present in normal or moderately high titres (mean: 2,900). Lymphocyte reactivity to VZV antigen was negative or weakly positive in 17 of the 20 patients. After 6 weeks, antibody titres rose significantly (mean: 36,000) and the lymphocyte response was highly positive in 11, weakly positive in 6, and remained negative in 3 patients. Thirty-three healthy adults ranging in age from 55-65 years with a negative VZV-specific CMI, but positive VZV antibodies (mean: 190), were immunized with the Oka-strain varicella vaccine (Varilrix). After 6 weeks, the mean antibody titre had only increased slightly (mean: 400). However, a positive VZV-specific CMI response occurred in 28 out of 33 subjects, while 5 remained negative. Therefore, conversion from a negative to a positive CMI response can be achieved by varicella vaccination of seropositive subjects. This raises the question whether booster vaccination of CMI-negative subjects could prevent zoster.