Vaccine-preventable infections in patients treated with cladribine tablets In the clinical trial program of cladribine tablets, the incidence rate of total infections [cladribine 24.9 versus placebo 27.1 events per 100 patient-years (PY)] and serious infections (0.8 versus 0.9/100 PY) were similar in patients receiving cladribine tablets and placebo. 56 Among the vaccine-preventable diseases, herpes zoster occurred more frequently on cladribine tablets compared with placebo (0.83 versus 0.2 episodes per 100 PY). 57 The incidence rate was higher in cladribine-treated patients with grade 3–4 lymphopenia (4.5/100 PY) versus grade 0–2 lymphopenia (0.73/100 PY). Most herpes zoster episodes occurred 1–3 years after the start of therapy. Severe or disseminated herpes zoster episodes have not been reported to date. Other observed vaccine-preventable diseases were limited to influenza, with similar incidence rates in the oral cladribine and placebo groups (2.75 versus 2.69 cases per 100 PY with lymphopenia grade 0–2; and 3.35 versus 2.69/100 PY with lymphopenia grade 3–4).