Immunogenicity and Safety of a Booster Vaccination With a Recombinant Protein RBD Candidate Vaccine Against SARS-CoV-2 in Healthy Adults Volunteers Fully Vaccinated Followed by an Extension Period to Study a Fourth Dose Administration.

Pregnant or lactating or intending to become pregnant or plans to breastfeed during the study.

Positive pregnancy test at Screening or vaccination day.

Any medical disease (acute, subacute, intermittent, or chronic) or condition that in the opinion of the Investigator compromises the subject's safety, preclude vaccination or compromises interpretation of the results.

Ongoing serious psychiatric condition likely to affect participation in the study (e.g., ongoing severe depression, recent suicidal ideation, bipolar disorder, personality disorder, alcohol and drug dependency, severe eating disorder, psychosis, use of mood stabilisers or antipsychotic medication).

History of respiratory disease (e.g., chronic obstructive pulmonary disease \[COPD\]) requiring daily medications currently or any treatment of respiratory disease exacerbations (e.g., asthma exacerbation) in the last 6 months.

History of significant cardiovascular disease (e.g., congestive heart failure, cardiomyopathy, ischemic heart disease) or history of myocarditis or pericarditis as an adult. Controlled hypertension will be permitted at the discretion of the Investigator.

History of neurological or neurodevelopmental conditions (e.g., epilepsy, stroke, seizures in the last 3 years, encephalopathy, focal neurologic deficits, Guillain-Barré syndrome, encephalomyelitis, or transverse myelitis).

Ongoing malignancy or recent diagnosis of malignancy in the last five years excluding basal cell and squamous cell carcinoma of the skin, which are allowed.

Any confirmed or suspected autoimmune, immunosuppressive or immunodeficiency disease/condition (iatrogenic or congenital), including human immunodeficiency virus (HIV) infection, asplenia, or recurrent severe infections.

Acute illness within 72 hours before vaccination day that, in the opinion of the Investigator may interfere the evaluation of safety parameters.

Received investigational drug within 90 days before Screening or plans to participate in another interventional clinical study (drug/biologic/device) within 12 months after vaccination.

History of hypersensitivity or severe allergic reactions, including anaphylaxis, generalised urticarial, angioedema and other significant reactions related to food, drugs, vaccines, or pharmaceutical agents, which are likely to be exacerbated by any component of the COVID-19 vaccine HIPRA.

Use of any immunosuppressant, glucocorticoids, or other immune-modifying drugs within 2 months before vaccination day; or anticipation of the need for immunosuppressive treatment within 182 days after vaccination.

Received immunoglobulin, blood-derived products, or other immunosuppressant drugs within 90 days before vaccination (Day 0).

Known disturbance of coagulation (iatrogenic or congenital) or blood dyscrasias.

Known bleeding disorder (e.g., factor deficiency, coagulopathy, or platelet disorder), (iatrogenic or congenital), blood dyscrasias, or prior history of significant bleeding or bruising following intramuscular (IM) injections or venepuncture.

Chronic liver disease.

Positive test for HIV types 1 or 2 infection, hepatitis B surface antigen (HBsAg), or hepatitis C virus antibodies (HCV Abs) at Screening.

Suspected or known current alcohol abuse or any other substances abuse (except tobacco).

History of COVID-19 infection.

Ever been included in a trial with an experimental vaccine against COVID-19.

Close contact with anyone known to have SARS-CoV-2 infection within 15 days before Screening.

Scheduled elective surgery during the study.

Life expectancy of less than 12 months.

Any condition and/or laboratory finding that, in the Investigators opinion, would interfere with the study or put the subject at risk.

History of anaphylactic shock of any kind

History of COVID-19 infection.

Pregnancy or breast-feeding at screening or Day 0

Participant has a clinically significant acute illness or fever (temperature ≥38º C / 100.4ºF) at screening or within 48 hours prior to the planned vaccination

Participant had a surgery requiring hospitalization before vaccination and he/she has not received the hospital discharge at day 0

Participant has any active malignancy

Participant has ongoing severe and non-stable psychiatric condition likely to affect participation in the study

Participant has a problematic or risk use of substances including alcohol that can compromise the study follow-up

Participant has a bleeding disorder, blood dyscrasia, or continuous use of anticoagulants or has any condition that contraindicates intramuscular injections or frequent phlebotomy

Participant has abnormal function of the immune system as in autoimmune diseases, asplenia, recurrent infections or congenital/acquired immunodeficiency

Chronic or recurrent administration (during at least 14 days) of systemic immunosuppressant medication within 12 weeks preceding the planned administration of study vaccine

Subject has received immunoglobulins and/or blood-derived products 12 weeks prior vaccination

Participant received any immunotherapy (monoclonal antibodies, plasma) aimed to prevent or treat COVID-19 within 90 days preceding the planned administration of study vaccine

Participation in any research involving an investigational product (drug, biologic, device) within 12 weeks prior to vaccination and during the study

Participant has donated ≥ 450ml of blood products within 12 weeks before screening

Participant has any medical condition and/or finding that in the investigator opinion might increase participant risks, interfere with the study or impair interpretation of study data

What this study is about