Vaccinations are among the most effective medical procedures and have had an incredible impact on almost everyone’s life. One of the populations that can benefit the most from them are elderly people. Unfortunately, in this group, vaccines are less effective than in other groups, due to immunosenescence. The immune system ages like the whole body and becomes less effective in responding to infections and vaccinations. At the same time, immunosenescence also favors an inflammatory microenvironment, which is linked to many conditions typical of the geriatrics population. The microbiota is one of the key actors in modulating the immune response and, in this review, we discuss the current evidence on the role of microbiota in regulating the immune response to vaccines, particularly in elderly people.

Gut microbiota (GM) comprises more than one thousand microorganisms between bacterial species, viruses, fungi, and protozoa, and represents the main actor of a wide net of molecular interactions, involving, among others, the endocrine system, immune responses, and metabolism. GM influences many endocrine functions such as adrenal steroidogenesis, thyroid function, sexual hormones, IGF-1 pathway and peptides produced in gastrointestinal system. It is fundamental in glycaemic control and obesity, while also exerting an important function in modulating the immune system and associated inflammatory disease. The result of this crosstalk in gut mucosa is the formation of the intestinal immunological niche. Visceral adipose tissue (VAT) produces about 600 different peptides, it is involved in lipid and glucose metabolism and in some immune reactions through several adipokines. GM and VAT interact in a bidirectional fashion: while gut dysbiosis can modify VAT adipokines and hormone secretion, VAT hyperplasia modifies GM composition. Acquired or genetic factors leading to gut dysbiosis or increasing VAT (i.e., Western diet) induce a proinflammatory condition, which plays a pivotal role in the development of dysmetabolic and immunologic conditions, such as diabetes mellitus. Diabetes is clearly associated with specific patterns of GM alterations, with an abundance or reduction of GM species involved in controlling mucosal barrier status, glycaemic levels and exerting a pro- or anti-inflammatory activity. All these factors could explain the higher incidence of several inflammatory conditions in Western countries; furthermore, besides the specific alterations observed in diabetes, this paradigm could represent a common pathway acting in many metabolic conditions and could pave the way to a new, interesting therapeutic approach.

Background: Refeeding syndrome (RS) is a neglected, potentially fatal syndrome that occurs in malnourished patients undergoing rapid nutritional replenishment after a period of fasting. The American Society for Parenteral and Enteral Nutrition (ASPEN) recently released new criteria for RS risk and diagnosis. Real-life data on its incidence are still limited. Methods: We consecutively enrolled patients admitted to the Internal Medicine and Gastroenterology Unit of our center. The RS risk prevalence and incidence of RS were evaluated according to ASPEN. The length of stay (LOS), mortality, and re-admission rate within 30 days were assessed. Results: Among 203 admitted patients, 98 (48.3%) were at risk of RS; RS occurred in 38 patients (18.7% of the entire cohort). Patients diagnosed with RS had a higher mean LOS (12.5 days ± 7.9) than those who were not diagnosed with RS (7.1 ± 4.2) (p < 0.0001). Nine patients (4.4%) died. Body mass index (OR 0.82; 95% CI 0.69–0.97), RS diagnosis (OR 10.1; 95% CI 2.4–42.6), and medical nutritional support within 48 h (OR 0.12; 95% CI 0.02–0.56) were associated with mortality. Conclusions: RS incidence is high among clinical wards, influencing clinical outcomes. Awareness among clinicians is necessary to identify patients at risk and to support those developing this syndrome.