This clinical trial is focused on studying the effects of a booster vaccination for COVID-19, a disease caused by the SARS-CoV-2 virus. The study involves two different vaccines. One is called Comirnaty Omicron XBB.1.5, which is a type of mRNA vaccine designed to protect against the Omicron variant of the virus. The other vaccine being studied is a new candidate called PHH-1V81, which is a recombinant protein vaccine. This means it uses a piece of the virus’s protein to help the body recognize and fight the virus.
The purpose of the study is to assess the safety and immune response of the PHH-1V81 booster in adults who have already received their initial COVID-19 vaccinations and at least one booster dose of an mRNA vaccine approved in the European Union. Participants will receive either the PHH-1V81 booster or the Comirnaty Omicron XBB.1.5 vaccine. The study will compare how well each vaccine works in boosting the immune system’s ability to fight the virus, particularly against the Omicron XBB.1.16 variant.
Throughout the study, participants will be monitored for any reactions or side effects after receiving the booster. The study will also measure the level of antibodies, which are proteins the body makes to fight infections, to see how well the vaccines work. The trial will help determine if the new PHH-1V81 vaccine is as effective as the existing Comirnaty vaccine in boosting immunity against COVID-19.



Spain