Inclusion Criteria:  Men and women, aged 65-89 years, who have received 2-3 doses of the same vaccine (Pfizer-BioNTech or Moderna) for more than 6 months, volunteered for a third dose of vaccine, had telephone or internet access, were able to provide informed consent, and lived <75 km from the CRC  Exclusion Criteria:  Patients with COVID-19 disease (clinical and serological data at post), with possibly affected cognitive functions (score < 12 on the Functional Activities Questionnaire (FAQ)), with allergies (soy, lactose, yeast, maltodextrin), with a chronically weakened immune system (AIDS...) or undergoing anti-cancer treatment (chemotherapy or radiotherapy) and who do not speak French or English.