Despite the widespread introduction of vaccines against Rotavirus, Rotavirus continues to be a cause of significant morbidity and mortality in the developing world. This study will assess protection against rotavirus infection and investigate immune correlates of protection following vaccination with a novel trivalent VP8 subunit rotavirus vaccine used alone or in combination with oral rotavirus vaccine.

This is a randomized, open-label clinical trial of Rotarix and trivalent VP8 subunit vaccine given alone or in combined schedules to 720 infants in Zambia at 6, 10 and 14 weeks followed by challenge at 18 weeks used to assess mucosal immunity.

Potential participants will be identified through antenatal and child health monitoring clinics in selected facilities in Lusaka Zambia. Interested parents will be invited to the clinical research site for informed consent procedures and assessment of eligibility. Children meeting the eligibility criteria with written informed consent for participation will be randomized to one of the four available study arms using simple randomization in block sizes of 8. Blood, stool, and saliva samples will be collected prior to completing vaccination according to randomization arm. All parents/guardians will be provided with post immunisation diary cards to document any reactions following vaccination. Trained study staff will contact parents and guardians of enrolled participants weekly to enquire on the child's health and assist with documentation of solicited reactions following vaccinations.

Enrolled children will be followed up for at least five months following enrollment. Follow up vaccinations will be provided each month until all children have completed all assigned study vaccinations. Upon completion of study vaccination, participants will be challenged with oral rotavirus vaccine, Rotarix TM to assess mucosal immunity.

Primary outcome:

The primary objective of the study will be to detect a reduction in the proportion of children shedding vaccine rotavirus in stool at any timepoint 5-9 days after challenge, among children immunized with P2-VP8 subunit vaccine alone or in combination with Rotarix, compared with infants receiving Rotarix alone. The primary outcomes will be prevalence of rotavirus (Rotarix) shedding at any timepoint in samples collected 5,7 and 9 days after challenge.

Secondary outcomes:

i.) Seroconversion following vaccination: Detection of an increase in seroconversion in either of the combined vaccination arms compared with Rotarix alone.

ii.) Immune boosting. We will compare the number of gut-homing (alpha 4 beta 7+) Immunoglobulin A (IgA) and Immunoglobulin G (IgG) rotavirus VP8-specific Antibody secreting cells (ASCs) 7 days after the third clinic visit in 50 infants from each study arm (i.e. after the first VP8 vaccine booster dose, after the third VP8 vaccine dose (alone or in combination with Rotarix), or after no vaccine (control) in the Rotarix only arm).

Inclusion Criteria:

• Healthy infants as established by medical history and physical examination.
• Infants will be 6-10 weeks old at time of enrollment
• parents plan to remain in the area for the duration of the study.
• Parent/guardian understands the study procedures and willing to provide informed consent to participate in the study

Exclusion Criteria:

• Acutely unwell
• Infant or infant's mother has syndromic or documented evidence of being immunocompromised (independent of HIV status)
• Known allergy to any vaccine component
• Previously received rotavirus vaccine
• Received immunosuppressive medication
• Major congenital or genetic abnormality
• Any condition in the parents/infant that, in the judgment of the investigator, would interfere with or serves as a contraindication to protocol adherence or a participant's parents' ability to give informed consent.
• Participant's parents not available or willing to accept active follow-up by the study staff

Communicate with the participants results of the study and plans to share de-identified data. Disseminate to internal research meetings as well as the Ministry of Health Zambia.

Submit manuscripts, publications, in peer review journal and also present at local and international scientific conferences

after study completion