The purpose of this study is to evaluate if the intestinal microbiota influences rotavirus vaccine immune responses in healthy adult volunteers.

This study will alter the intestinal microbiota in healthy adults using antibiotics and subsequently measure immune reactions to the rotavirus vaccine (Rotarix), the tetanus vaccine and the pneumococcal vaccine (Pneumo23).

Inclusion Criteria:

• Healthy, as determined by a responsible physician, based on a medical evaluation including medical history, physical examination and laboratory tests carried out within 28 days prior to starting antibiotics (day -98). A subject with a clinical abnormality or laboratory parameter outside the reference range may be included if the investigator agrees that the finding is unlikely to introduce additional risk factors and will not interfere with the study procedures
• Male between 18 and 35 years of age, inclusive at the time of signing the informed consent
• Capable of giving written informed consent and able to comply with the requirements and restrictions listed in the informed consent form
• Normal defecation pattern (defined as ≤3x/ day and ≥3x/week)

Exclusion Criteria:

• Subject has had a major illness in the past 3 months or any significant chronic medical illness that the investigator would deem unfavorable for enrollment, including inflammatory diseases.
• Subject with any history of immunodeficiency
• Subjects with a history of any type of malignancy
• Subject with a history of thrombocytopenia or bleeding disorder
• Subject has a past or current gastrointestinal disease which may influence the gut microbiota
• Current or chronic history of liver disease, or known hepatic or biliary abnormalities (with the exception of Gilbert's syndrome or asymptomatic gallstones)
• History of alcoholism and/or drinking more than an average of 5 units of alcohol per day
• The subject has received an investigational product within three months of day 0 of the current study