The purpose of this study is to compare the number of responders to vaccination with the influenza virus vaccine at different time points after last dose of rituximab in patients with lymphoma. Secondly to study the immune-response to vaccination with influenza virus vaccine, after treatment with rituximab in relation to the reconstitution of immune-function.

Inclusion Criteria:

1. Patients with non-Hodgkin's lymphoma, treated with rituximab (with a range of 6-12 cycles) and who are in remission.
2. Completion of rituximab therapy in the last twelve months before start of the study.
3. Age ≥ 18 years.
4. Signing of informed consent.

Exclusion Criteria:

1. Completion of rituximab therapy 7-8 months before start of the study.
2. Fever at time of vaccination.
3. Previous/known allergic reaction to any of the components of the vaccines given.