Varicella vaccination in pediatric oncology patients without interruption of chemotherapy

Background: Morbidity and mortality from primary varicella-zoster virus (VZV) infection is increased in immunocompromised children. Vaccination of VZV-seronegative cancer patients with live-attenuated varicella vaccine is safe when chemotherapy is interrupted. However, VZV vaccination without interruption of chemotherapy would be preferable. Objective: To vaccinate VZV-seronegative pediatric oncology patients with live-attenuated VZV vaccine without interrupting their chemotherapy. Study-design: We performed a single-center prospective cohort study. Results: Thirty-one patients with either a hematological malignancy (n=24) or a solid tumor (n=7) were vaccinated early during their course of chemotherapy. VZV IgG seroconversion occurred in 14 of the 31 patients (45%) after one vaccination. Only 20 patients were revaccinated after 3 months. These were patients who did not seroconvert (5 patients) and patients who serocoverted (15 patients) to induce or sustain seropositivity. Of these 20 patients the final seroconversion rate was 70%. Seven out of the 31 patients (23%) developed a mild rash of which 5 were treated with antivirals and recovered completely without interrupting chemotherapy, and 2 recovered untreated. Of these 31 immunized patients 26 were available for cellular testing. After one vaccination 20 of 26 patients (77%) tested positive for VZV-specific CD4⁺ T cells, of which 7 patients had remained VZV-seronegative. After the second vaccination 11 of 11 patients showed VZV-specific CD4⁺ T cells to sustain positivity, although 4 remained VZV-seronegative. Conclusions: This study indicates that live-attenuated VZV vaccine can be safely administered to closely monitored pediatric oncology patients without interruption of chemotherapy and adaptive immunity was induced despite incomplete seroconversion.