Evaluation of pandemic H1N1 (2009) influenza vaccine in adults with solid tumor and hematological malignancies on active systemic treatment

Background: Over 85% of healthy individuals vaccinated with the pandemic H1N1 (pH1N1) vaccine achieve seroprotection.

Objectives: We evaluated the safety and immunogenicity of pH1N1 vaccine in patients undergoing chemotherapy for hematological and solid tumor malignancies.

Study design: Adult patients, receiving chemotherapy undergoing pH1N1 vaccination at our institution had blood samples drawn for CBC (baseline only) and serology prior to and ≥ 21 days post vaccination. HAI antibody testing was performed for pH1N1 (A/California/7/2009 strain) and seasonal H1 (A/Brisbane/59/07 strain). Seroprotection was defined as a pH1N1 antibody titre ≥ 1:40 and seroconversion as an antibody titre >4 × baseline. Patients completed a symptom diary card.

Results: Paired samples were available for 46 patients (20 solid tumor, 26 hematological), median age 56 (range 23-76) years. The seroprotective rate post-vaccination for solid tumors was 50% compared to 27% for hematological malignancy (p=0.11), respective seroconversion rates were 45% and 19% (p=0.06). In patients with solid tumors vaccination mid cycle resulted in the highest pH1N1 titres, although timing and blood count were not associated with seroconversion or seroprotection. For hematological patients, a normal leukocyte count and vaccination at the beginning of a cycle were associated with higher rates of seroconversion (p ≤ 0.05). Addition of rituximab to chemotherapy resulted in a failure to seroconvert (p=0.05). Vaccination was well tolerated by all patients.

Conclusions: Although well tolerated, the seroprotection rate following pH1N1 vaccination is lower than that would be expected. Further investigation into immunization strategies in patients receiving chemotherapy is required.