After giving their informed consent, the study subjects will complete screening procedures to assess their eligibility for the study (Visit 1). Participants deemed suitable for the study will be randomized into two study arms (placebo, probiotic) before undergoing a baseline visit (Visit 2) before the start of the intervention period. During the 6-month intervention period, the participants will attend study visits at 3 months (Visit 3) into the intervention as well as at the end of intervention (at 6 months, Visit 4). Blood, saliva, and faecal samples will be collected at visits 2-4. In addition to sampling, during the whole intervention period, the participants will fill out a weekly questionnaire in which they are asked to record any possible symptoms of COVID-19. The participants' dietary habits are assessed via a food frequency questionnaire (FFQ) before the start of the intervention period. Also, the participants are asked to maintain their habitual diet and lifestyle as well as not to consume any other probiotic or prebiotic supplements.
This study will explore how a well-known probiotic strain L. reuteri DSM 17938 impacts SARS-CoV-2 specific antibody response upon and after infection in healthy adults.