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Imprinting of the specific molecular image of a given protein antigen into immunological memory is one of the hallmarks of immunity. A later contact with a related, but different antigen should not trigger the memory response (because the produced antibodies would not be effective). The preferential expansion of cross-reactive antibodies, or T-lymphocytes for that matter, by a related antigen has been termed the original antigenic sin and was first described by Thomas Francis Jr. in 1960. The phenomenon was initially described for influenza virus, but also has been found for dengue and rotavirus. The antibody dependent enhancement observed in feline coronavirus vaccination also may be related to the original antigenic sin. For a full interpretation of the effectivity of the immune response against SARS-CoV-2, as well as for the success of vaccination, the role of existing immunological memory against circulating corona viruses is reviewed and analyzed.

Data on characteristics of clinical trials with probiotics, registered at ClinicalTrials.gov were retrieved from the registry . Data on the registration process itself (moment of registration of the trial in relation to date of inclusion of first participant, data of completion of the study) as well as the number of participants were analysed. A trend analysis (over the period 2000-2020) was made of the number of participants in clinical trials with probiotics on gastrointestinal conditions and diseases. A comparison was made between conditions and diseases studied in completed clinical trials with those trials not yet recruiting participants. The data can be used and reused for assessment of the quality of clinical studies with probiotics and to identify future trends in applications of probiotics.

Over 1,000 clinical studies with probiotics, registered at ClinicalTrials.gov and/or the International Clinical Trials Registry Platform (ICTRP) of the World Health Organization, have addressed over 700 different diseases and conditions. The average size of a clinical trial with probiotics (74 participants) is comparable to the overall average of all studies in ClincialTrials.gov. Lactobacillus rhamnosus GG (LGG) and Bifidobacterium animalis ssp. lactis BB12 are the probiotic strains studied most. The exact composition of the product which is used, including the dosage, is not always indicated in the registry. The majority of probiotics studies at ClinicalTrials.gov is registered in the USA or Europe (56%). The data from ICTRP show the rapid expansion of clinical studies with probiotics in Asia, notably Iran and China.

In severe humoral immunodeficiency the indication for antibody replacement therapy (ART) is clear, and supported by several large studies. However, for milder forms of humoral immunodeficiency, the indication for ART is less clear. This is a retrospective cohort study of 87 adults with recurrent respiratory tract infections who received ART. The patients had severe or mild humoral immunodeficiency, and were followed up for a median of 62 months. Infection frequency, pharmacy-registered antibiotics use and hospital admissions significantly decreased under ART compared to the year prior to starting ART (median 5.50 (anamnestically)–0.82 (physician-confirmed) infections/year, p