inclusion criteria: 1. age ≥ 18 years, of which 50% and 20% were aged ≥60 years in phase ii and phase iii studies, respectively, regardless of previous sars-cov-2 infection status, with proof of four doses of any monovalent vaccine against covid-19, of which the last dose administered at least 120 days to 540 days ago. 2. if pre-existing medical conditions: be in a stable condition that does not require hospitalization or significant changes in therapy during the three months prior to enrollment. 3. agree to regular contact by phone, electronic means, and/or home visits. 4. intention to participate in the study, documented by the informed consent form.

inclusion criteria: 1. age ≥ 18 years, of which 50% and 20% were aged ≥60 years in phase ii and phase iii studies, respectively, regardless of previous sars-cov-2 infection status, with proof of four doses of any monovalent vaccine against covid-19, of which the last dose administered at least 120 days to 540 days ago. 2. if pre-existing medical conditions: be in a stable condition that does not require hospitalization or significant changes in therapy during the three months prior to enrollment. 3. agree to regular contact by phone, electronic means, and/or home visits. 4. intention to participate in the study, documented by the informed consent form.

inclusion criteria: age ≥ 18 years, of which 50% and 20% were aged ≥60 years in phase ii and phase iii studies, respectively, regardless of previous sars-cov-2 infection status, with proof of four doses of any monovalent vaccine against covid-19, of which the last dose administered at least 120 days to 540 days ago. if pre-existing medical conditions: be in a stable condition that does not require hospitalization or significant changes in therapy during the three months prior to enrollment. agree to regular contact by phone, electronic means, and/or home visits. intention to participate in the study, documented by the informed consent form.

inclusion criteria: age ≥ 18 years, of which 50% and 20% were aged ≥60 years in phase ii and phase iii studies, respectively, regardless of previous sars-cov-2 infection status, with proof of four doses of any monovalent vaccine against covid-19, of which the last dose administered at least 120 days to 540 days ago. if pre-existing medical conditions: be in a stable condition that does not require hospitalization or significant changes in therapy during the three months prior to enrollment. agree to regular contact by phone, electronic means, and/or home visits. intention to participate in the study, documented by the informed consent form.

inclusion criteria: age ≥ 18 years, of which 50% and 20% were aged ≥60 years in phase ii and phase iii studies, respectively, regardless of previous sars-cov-2 infection status, with proof of four doses of any vaccine against covid-19, of which the last dose administered at least 120 days to 240 days ago. if pre-existing medical conditions: be in a stable condition that does not require hospitalization or significant changes in therapy during the three months prior to enrollment. agree to regular contact by phone, electronic means, and/or home visits. intention to participate in the study, documented by the informed consent form.

inclusion criteria: age ≥ 18 years, of which 50% and 20% were aged ≥60 years in phase ii and phase iii studies, respectively, regardless of previous sars-cov-2 infection status, with proof of four doses of any vaccine against covid-19, of which the last dose administered at least 120 days to 240 days ago. if pre-existing medical conditions: be in a stable condition that does not require hospitalization or significant changes in therapy during the three months prior to enrollment. agree to regular contact by phone, electronic means, and/or home visits. intention to participate in the study, documented by the informed consent form.

inclusion criteria: age ≥ 18 years, of which 50% and 20% were aged ≥60 years in phase ii and phase iii studies, respectively, regardless of sars-cov-2 infection status, with proof of two or more doses of inactive adsorbed vaccine against covid-19, azd1222 (chadox1), or vaccine against covid-19 bnt162b2 with or without a booster of vaccine against covid-19 bnt162b2 or inactive adsorbed vaccine against covid-19, of which the last dose administered at least 120 days ago. if pre-existing medical conditions: be in a stable condition that does not require hospitalization or significant changes in therapy during the three months prior to enrollment. agree to regular contact by phone, electronic means, and/or home visits. intention to participate in the study, documented by the informed consent form.

inclusion criteria: age ≥ 18 years, of which 50% and 20% were aged ≥60 years in phase ii and phase iii studies, respectively, regardless of sars-cov-2 infection status, with proof of two or more doses of inactive adsorbed vaccine against covid-19, azd1222 (chadox1), or vaccine against covid-19 bnt162b2 with or without a booster of vaccine against covid-19 bnt162b2 or inactive adsorbed vaccine against covid-19, of which the last dose administered at least 120 days ago. if pre-existing medical conditions: be in a stable condition that does not require hospitalization or significant changes in therapy during the three months prior to enrollment. agree to regular contact by phone, electronic means, and/or home visits. intention to participate in the study, documented by the informed consent form.