inclusion criteria: * volunteer healthcare worker with any valid credential of the center * 25 years old and over * not having been diagnosed with covid-19 * a healthy individual as per investigator's judgment or stating stable non-transmissible chronic disease without hospitalization in the last year, without change of medications or addition of medications to treat chronic illnesses in the last 3 months. * no pregnancy or breastfeeding * female subjects of childbearing potential using an effective family planning method or surgical sterilization or not sexually active during the study * do not drink more than 300 ml of tea a day * do not take supplements or products containing egcg during the study * being able to set aside time each day to complete the study questionnaires * being able to read and understand the informed consent form before the study

inclusion criteria: * volunteer healthcare worker with any valid credential of the center * 25 years old and over * not having been diagnosed with covid-19 * a healthy individual as per investigator's judgment or stating stable non-transmissible chronic disease without hospitalization in the last year, without change of medications or addition of medications to treat chronic illnesses in the last 3 months. * no pregnancy or breastfeeding * female subjects of childbearing potential using an effective family planning method or surgical sterilization or not sexually active during the study * do not drink more than 300 ml of tea a day * do not take supplements or products containing egcg during the study * being able to set aside time each day to complete the study questionnaires * being able to read and understand the informed consent form before the study

inclusion criteria: - volunteer healthcare worker with any valid credential of the center - 25 years old and over - not having been diagnosed with covid-19 - a healthy individual as per investigator's judgment or stating stable non-transmissible chronic disease without hospitalization in the last year, without change of medications or addition of medications to treat chronic illnesses in the last 3 months. - no pregnancy or breastfeeding - female subjects of childbearing potential using an effective family planning method or surgical sterilization or not sexually active during the study - do not drink more than 300 ml of tea a day - do not take supplements or products containing egcg during the study - being able to set aside time each day to complete the study questionnaires - being able to read and understand the informed consent form before the study

inclusion criteria: - volunteer healthcare worker with any valid credential of the center - 25 years old and over - not having been diagnosed with covid-19 - a healthy individual as per investigator's judgment or stating stable non-transmissible chronic disease without hospitalization in the last year, without change of medications or addition of medications to treat chronic illnesses in the last 3 months. - no pregnancy or breastfeeding - female subjects of childbearing potential using an effective family planning method or surgical sterilization or not sexually active during the study - do not drink more than 300 ml of tea a day - do not take supplements or products containing egcg during the study - being able to set aside time each day to complete the study questionnaires - being able to read and understand the informed consent form before the study