Non-specific Effects of FLU-MMR Vaccines in Adults

Inclusion Criteria: To be eligible to participate in this study, the participant must meet the following criteria: • Be older than 18 years old. Observation: the elderly is at risk for severe forms of COVID-19, therefore, the evidence in this age group is very relevant. However, they can also be a first priority population to receive a specific vaccine, limiting the time to follow-up on the study. In addition, influenza and MMR vaccines can lead to a lower immune system in the elderly than in young people. Therefore, it is likely that a more rational choice will be to carry out the study in a young population. Exclusion Criteria: Participants will not be included in the study if they present (reported by the research participants): * Known allergy to components of influenza and MMR vaccines or serious adverse events to previous administration. * Fever (\> 38 degrees Celsius) in the last 24 hours. * Pregnancy. Note: pregnancy should be avoided for one month after vaccination. * Symptoms of active viral or bacterial infection. * Documented diagnosis of COVID-19. * Vaccination in the last 4 weeks against SARS-CoV-2. * Immunocompromised participants. This exclusion category includes: a) infection with the human immunodeficiency virus (HIV-1); b) neutropenic participant with less than 500 neutrophils/mm3; c) participant with organ transplantation; d) participants with bone marrow transplantation; e) participants in chemotherapy treatment; f) participants with primary immunodeficiency; g) participants with severe lymphopenia with less than 400 lymphocytes/mm3; h) treatment with any anti-cytokine medication; i) treatment with oral or intravenous steroids, for example, daily doses of prednisone or equivalent for more than 3 months, or probable use of oral or intravenous steroids within next four weeks. * Some type of lymphoma or malignancy in the previous two years. * Direct involvement in the design or execution of the study. * Absence from work for more than 4 weeks within the next 12 weeks after study admission (vacation, maternity leave, retirement, planned surgery, etc.)