There are limited studies assessing the live attenuated varicella vaccine following alloHCT. Due to the morbidity of varicella acquired after childhood, we immunized and retrospectively analyzed the safety and immunogenicity of this vaccine in 46 VZV seronegative patients <20 years old at HCT who achieved a CD4 cell count ≥200/ul, were off immunosuppression, and responded to ≥1 post HCT vaccines. Two vaccinated patients lacking follow-up titers were excluded from analysis. Stem cells were derived from an HLA-matched sibling (n=18) or an alternative (HLA MM related or unrelated) donor (n=26). Median time to vaccination was 4 years. Sixty-four percent of patients seroconverted following one immunization. There was no significant difference in response between recipients of a matched related or alternative donor graft (p=0.2) or between those given a TCD or T-replete alternative donor graft (p=0.27). Three of 44 patients developed a self-limited varicella-like rash within 2.5 weeks of immunization. With a median follow-up of 29.1 (range: 6.9-167.1 ) months, there were no subsequent cases of varicella-like rashes. No patient developed shingles. This study suggests that this vaccine is safe and immunogenic when given according to pre-set clinical and immunologic milestones, warranting larger prospective studies in patients ≥24 months following HCT as outlined in current post HCT vaccine guidelines.

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1282 In 2005, in an effort to reduce the increasing incidence of pertussis in adolescents and adults, two vaccines containing tetanus, reduced diphtheria and acellular pertussis toxoids (Tdap) were approved for this population. Although both vaccines contain similar amounts of tetanus and diphtheria toxoid, they vary in their pertussis toxoid(PT) content (2.5 vs 8 mcg/dose). In 2006, the Advisory Committee on Immunization Practices recommended that all adolescents and adults receive a single dose of Tdap. In 2008, we reported at this meeting an evaluation of the Tdap containing 2.5 mcg/dose approved for individuals 11–64 years of age. Although response to tetanus was 71% when this vaccine was given as a booster, only 7 of 41 patients responded to PT, 6 of whom were children. This poor response was likely due in part to the low dose of PT and the limited numbers of pertussis specific memory T and B cells potentially transferred from the stem cell donor. At the end of 2008, the upper age limit for Tdap containing 8 mcg PT/dose was extended from 18 years of age to 64 years. We now report response to this vaccine in 64 alloHSCT recipients (20 children, 44 adults). Patients were transplanted for the treatment of acute (n=31) or chronic (n=6) leukemia, lymphoma (n=16), MDS (n=5), multiple myeloma (n=3), or other (n=3). Forty-four pts were > 18 yrs of age at time of transplant and 20 were < 18 yrs of age. Stem cell donors were an HLA matched sibling (n=31), HLA mismatched related (n=4), or unrelated adult (n=18) or unrelated cord blood (n=11) donor. Forty-four percent of patients received a T-cell-depleted allograft. Patients were a median age of 34 years at transplant and 36 years at vaccination. Over 90% of patients had pre vaccine PT of less than 2 IU/ml. Patients received one (n=47), two (n=15),or three (n=2) immunizations. Of pts receiving more than one vaccine, the median time to a second Tdap was 153 days (range 28–390). There were no severe local or systemic reactions in any recipient of Tdap including those who received > 1 vaccine. Response was defined as seroconversion > 5 IU/mL or >2 fold rise in PT titer for seropositive patients. Of the 63 patients evaluable after a single Tdap, 9 of 20 children and 9 of 43 adults responded (p=0.04) Response was associated with younger age, receipt of an unmodified transplant, and non-myeloablative or reduced intensity conditioning. None of the 11 UCBT recipients responded to a single Tdap. Currently, 9 of 12 patients evaluable for response following a second or third Tdap responded, including 2 of 3 UCBT recipients. In the last decade, pertussis in adolescents and adults has steadily increased with an estimated incidence of 800,000 to 3.3 million cases/year. Our studies suggest that use of Tdap containing 8 mcg/dose is preferable in alloHCT recipients and that administration of >1 Tdap is safe and often necessary to elicit pertussis immunity in this vulnerable patient population. Disclosures: No relevant conflicts of interest to declare.