* participants with unstable pre-existing medical conditions over the three months before enrollment (condition that has worsened to require hospitalization or significant changes in therapy). * planned administration/administration of a vaccine not foreseen by the study protocol from within 45 days before the first dose of study vaccine. * previous vaccination with any covid-19 vaccine. * history of covid-19 disease. * history of allergic reactions or anaphylaxis to previous immunizations or allergies to any components of the vaccine. * planning to become pregnant or planning to discontinue contraceptive precautions during the vaccination phase through 6 months after the second immunization. * history of bleeding disorders/hemostasis or use of anticoagulants. * currently having cancer or undergoing cancer treatment. * chronic administration (defined as more than 14 days) of immunosuppressants or other immune-modifying drugs within 3 months prior to the first vaccine dose (inhaled and topical steroids are allowed). * women who are pregnant or breastfeeding.

* participants with unstable pre-existing medical conditions over the three months before enrollment (condition that has worsened to require hospitalization or significant changes in therapy). * planned administration/administration of a vaccine not foreseen by the study protocol from within 45 days before the first dose of study vaccine. * previous vaccination with any covid-19 vaccine. * history of covid-19 disease. * history of allergic reactions or anaphylaxis to previous immunizations or allergies to any components of the vaccine. * planning to become pregnant or planning to discontinue contraceptive precautions during the vaccination phase through 6 months after the second immunization. * history of bleeding disorders/hemostasis or use of anticoagulants. * currently having cancer or undergoing cancer treatment. * chronic administration (defined as more than 14 days) of immunosuppressants or other immune-modifying drugs within 3 months prior to the first vaccine dose (inhaled and topical steroids are allowed). * women who are pregnant or breastfeeding.

- participants with unstable pre-existing medical conditions over the three months before enrollment (condition that has worsened to require hospitalization or significant changes in therapy). - planned administration/administration of a vaccine not foreseen by the study protocol from within 45 days before the first dose of study vaccine. - previous vaccination with any covid-19 vaccine. - history of covid-19 disease. - history of allergic reactions or anaphylaxis to previous immunizations or allergies to any components of the vaccine. - planning to become pregnant or planning to discontinue contraceptive precautions during the vaccination phase through 6 months after the second immunization. - history of bleeding disorders/hemostasis or use of anticoagulants. - currently having cancer or undergoing cancer treatment. - chronic administration (defined as more than 14 days) of immunosuppressants or other immune-modifying drugs within 3 months prior to the first vaccine dose (inhaled and topical steroids are allowed). - women who are pregnant or breastfeeding.

- participants with unstable pre-existing medical conditions over the three months before enrollment (condition that has worsened to require hospitalization or significant changes in therapy). - planned administration/administration of a vaccine not foreseen by the study protocol from within 45 days before the first dose of study vaccine. - previous vaccination with any covid-19 vaccine. - history of covid-19 disease. - history of allergic reactions or anaphylaxis to previous immunizations or allergies to any components of the vaccine. - planning to become pregnant or planning to discontinue contraceptive precautions during the vaccination phase through 6 months after the second immunization. - history of bleeding disorders/hemostasis or use of anticoagulants. - currently having cancer or undergoing cancer treatment. - chronic administration (defined as more than 14 days) of immunosuppressants or other immune-modifying drugs within 3 months prior to the first vaccine dose (inhaled and topical steroids are allowed). - women who are pregnant or breastfeeding.