We evaluated the clinical efficacy of long-term low-dose acyclovir prophylaxis for VZV infection after allogeneic PBSCT at the Princess Margaret Hospital (PMH), Canada and the Kyungpook National University Hospital (KNUH), Korea. The acyclovir prophylaxis regimen at PMH was acyclovir 400 mg/d orally until engraftment, and at KNUH was acyclovir 800 mg/d orally until immunosuppression discontinuation. Long-term acyclovir prophylaxis was given to 26/193 (14%) patients in the PMH group and 73/79 (92%) patients in the KNUH group.
In the PMH group, 42 cases (22%) developed VZV infection, while six cases (8%) had VZV infection in the KNUH group (p = 0.005). With a median of 26.5 months of follow-up, the incidences of VZV infection at one and two yr were 15.8% and 20.7% in the PMH group, and 2.5% and 5.8% in the KNUH group, respectively (p = 0.001). By controlling the other potential risk factors for VZV infection in multivariate analysis, the use of long-term acyclovir was the only protective factor for VZV infection after allogeneic PBSCT (p = 0.04, hazard ratio = 0.296). Long-term use of acyclovir appears to be protective for VZV infection after allogeneic PBSCT, especially during the period of immunosuppressive therapy.