The vaginal microbiome plays a crucial role in women's health and reproduction, impacting not only women but also their partners and children. However, its ecology and primary colonizers are not well understood. This study aims to explore the origin and heredity of the vaginal microbiome using a citizen science approach. The researchers will assemble a cohort of 100 networks, each with a central participant and 2 to 15 co-participants, totaling up to 500 participants. Participants will provide vaginal or penis swabs, complete questionnaires, and central participants will also donate stool samples. Girls under 18 may participate as co-participants if their mothers are enrolled, with first-void urine samples as an alternative method. Male partners can be included if they have intimate contact with central participants, but male family members and friends will not be part of the study. In the first phase, shared microbial strains along the gut-vagina axis and within the intimate microbiomes of participants from the same and different networks will be assessed. Transmission pathways will also be examined. Additionally, the metabolic environment in the vagina will be characterized. In the second phase, central participants will self-collect weekly vaginal swabs at three time points per year over five years. This phase will provide insights into the persistence and stability of the vaginal microbiome and the vaginal metabolic environment. If consent is given, genetic data from metagenomic sequencing will be analyzed to focus on variations related to the colonization, transmission, and persistence of microbial strains. This study will offer valuable insights into the origins, transmission, and long-term dynamics of the vaginal microbiome.

Inclusion Criteria of Central Participants:

• Adults aged 18 and over at the time of enrollment;
• Sex: Female;
• Pre-menopausal;
• Self-reported good health (including the absence of general infection) at the beginning of the study;
• Living in Belgium;
• Sufficient knowledge of the Dutch language;
• Consent form signed;
• Participating alongside her mother and at least one additional co-participant in the study.

Exclusion Criteria of Central Participants:

• Current pregnancy or planned pregnancy at the beginning of the study;
• Current diagnosis of cancer and/or immunosuppressive therapy in the 6 months before the study;
• Clinically significant abnormalities of the reproductive organs or any other medical condition at the discretion of the principal investigator;
• Use of oral/vaginal antibiotics/antifungals in the 2 months before the beginning of the study;
• Use of oral/vaginal pre-, pro-, post- and/or synbiotics in the 2 weeks before the beginning of the study;
• Vaginal showering during the study;
• Participation in an intervention study.

Inclusion Criteria of Co-participants:

• Closely related to or interacting with the central participant of the network at least during the last six months or more before the study, e.g. her mother, aunts, female cousins, sisters, daughters, housemates, partners or close friends;
• Aged 18 or over at the time of enrollment; OR 10 or over if the co-participant's mother is also participating in the study;
• Sex: Female; OR male aged 18 and over who is the partner or one of the partners (in case of polygamous relationships) of the central participant;
• Self-reported good health (including the absence of general infection);
• Sufficient knowledge of the Dutch language;
• Consent form signed.

Exclusion Criteria of Co-participants:

• Use of oral/vaginal antibiotics/antifungals in the 2 months before the study;
• Parallel participation in an intervention study;
• Vaginal showering during the study;
• Clinically significant abnormalities of the reproductive organs or any other medical condition that, in the opinion of the principal investigator, warrants exclusion from the study.

Central participants and co-participants will primarily be female. Male partners may be included if they have intimate contact with central participants, but male family members and friends will not be part of the study.

Central participants and their co-participants must live in Belgium.