Introduction Influenza is a potentially serious infection among hematooncology patients. The Immune system in these patients has been suppressed, and the antibody response to vaccines is supposed very poor. We conducted this study for the purpose of evaluating the immunogenicity and reactogenicity of the pandemic vaccine among immunocompromised hematooncology patients.

Materials and Methods During the 2009–2010 influenza season, 50 hematooncology patients (20 men, 30 women; mean age: 58.5±13.8 years) received two doses of monovalent inactivated unadjuvanted vaccine. The immunogenicity of the vaccine was evaluated according to conventionally used international criteria (EMEA, 1997; FDA, 2007).

Results The geometric mean of HI titre 4 weeks after vaccination increased from a pre-vac level of 5.0 to 12.0 for the first injection, and to 21.0 for the second injection. Both the sero-conversion and protection rates were 27% for the first injection, and 46% for the second injection. Within 1 year dosages of the rituximab (anti-CD20 monoclonal antibodies) decreased sero-response rates significantly, showing that rituximab had invalidated the vaccine's efficacy. No unique adverse events were detected.

Conclusions Although the immune system in hematooncology patients has been suppressed, a two-shot influenza vaccination series showed a booster effect and achieved the EMEA criteria. Dosages of rituximab invalidated the vaccine's efficacy within one year. Therefore, optimal timing for influenza vaccination is needed for patients receiving chemotherapy.