Introduction: The National Cancer Comprehensive Network (NCCN) recommends pneumococcal vaccination in all adults with newly diagnosed malignancy. Invasive pneumococcal infections in patients with active malignancy have been associated with a mortality risk up to 50%. Seventy-two percent of such infections have serotypes covered by the Pneumovax 23 (PPSV23) and Prevnar 13 (PCV13) vaccinations, suggesting the majority of such infections are preventable. The effects of chemotherapy on the efficacy of pre-chemotherapy vaccination have seldom been evaluated. Study Design: This study assessed titer levels of PPSV23 and PCV13 in all cancer patients over 18 years old who received the vaccines within 4 weeks of starting chemotherapy. Pneumococcal titers were obtained at 3-12 months after chemotherapy cessation. Results: Currently, 40 patients have enrolled with a target population of 50. The predominate diagnosis is breast cancer comprising 71% with 6% hematologic malignancies. The average time from cessation of chemotherapy to titer evaluation is 196 days. Interim analysis shows 55% of all titers assessed are below the lower limit of normal (LLN). Notably, 12.9% of all titers are not detectable. Nine percent of patients had at least 10 titers that were not detectable after chemotherapy containing taxol. Titers specific to AB 4, 2, 22, and 4G,S were below the lower limit of normal in over 75% of patients. Of the 37 titers assessed, patients on average had 19 below the LLN and 2 titers that were undetectable. With a historical adequate response criteria requiring a titer level 4 times the LLN in 50% of serotypes tested, no patients have had an adequate response to vaccination. Discussion: While receiving chemotherapy, patients are at increased risk for developing fatal pneumococcal infections due to their immunosuppression. Preliminary data from this study indicate that after cessation of chemotherapy and providing on average 6 months for recovery, over half of all titers are below the lower limit of normal. No patients thus far have met adequate response criteria to vaccination. It is likely that this response is insufficient to protect patients from future pneumococcal infection, and they may all benefit from revaccination. Determining the utility of revaccination after completion of chemotherapy merits further study.