The Vaccination Cohort Study on:
1. Immunologic Protection after Vaccination of Immune-compromised Patients
2. Assessment of the Infection Rate after International Travel

Individuals with immune deficiencies are at increased risk for infectious
diseases compared to general population. In addition, the responsiveness after
immunization can be diminished due to impaired function of monocytes, B cells
and/or T cells as well as other co-morbidity and the use of certain
immunosuppressive drugs . Exposure to infectious pathogens sharply increases
during travel, especially if people travel to tropical destinations. The aim of
this study is to investigate the cellular and humoral immune response after
vaccination of the immunecompromised host and to investigate travel related
infections in general.

This study has two goals:
1. Investigate the cellular and humoral immune response of immune compromised
travellers compared to the healthy traveller.
2. Investigate the epidemiology of travel related infectious diseases in a
population of dutch travellers

This will be a longitudinal observational cohort study. Potential candidates
will receive a letter at least one week prior to their visit to the travel
clinic containing information about the study and a patient information
document. Questions about the study can be asked during the first visit.
Inclusion to the study will only take place after signing the informed consent
document. Thereafter, the participant is asked to donate two peripheral blood
samples of 5 ml at three of four time points in this study as well as one
urinal and one fecal sample at two time points if patients travel to a
destination outside Europe or the United States/Canada (moments can overlap).
In addition, persons are asked to keep a diary during their travel, noting only
possible infectious events (fever, illness, contact with ill persons).
Participation in the study is terminated when all samples are collected or when
the patient decides to opt out. In practice, participation will not exceed the
duration of 12 months.

Blood samples:
1 Before vaccination (null serum).
2 Four weeks after vaccination (optimal time interval to measure immune
response) or after return from travel (to measure seroconversion to certain
infections, depending on the travel history).
4 After 9-12 months (to assess waning of the immune response).

Urine and fecal samples:
1 Prior to travel.
2 After returning from travel.

Study participants will donate 10 ml of blood at three visits to the travel
clinic. In case of a trip outside Western Europe, participants will be asked to
a collect a faecal and urinal sample before and after their journey. In
addition, study participants will be asked to keep a diary during their trip to
assess the rate of possible exposure to infectious pathogens.