A Randomized, Double-blind, Placebo-controlled Study on the Effects of Yeast ß-Glucan on the Incidence of Upper Respiratory Tract Infections and Immune Markers in Children

INTERVENTION: Experimental Group 1:Yeast ß‐Glucan Comple XBeverage;Experimental Group 2:Yeast ß‐Glucan Beverage;Placebo Group:Placebo beverage free of the aforementioned active ingredients; CONDITION: Upper Respiratory Tract Infection PRIMARY OUTCOME: Incidence of upper respiratory tract infection; SECONDARY OUTCOME: Pediatric Rhinoconjunctivitis Quality of Life Questionnaire;Adverse Events and Serious Adverse Events;Time to first upper respiratory tract infection;Total Nasal Symptom Score;Children Acute Respiratory Infection Symptoms score;Cumulative number of upper respiratory tract infections;Salivary secretory immunoglobulin A (sIgA) level; INCLUSION CRITERIA: 1.Aged 3–12 years, both males and females; 2.Have experienced >=3 episodes of upper respiratory tract infections in the past 12 months; 3.Willing and able to complete non‐invasive saliva sample collection; 4.The informed consent form signed by legal guardians;