Vaccine protection depends on a specific adaptive immune memory. However, a little-explored aspect of certain live vaccines may provide beneficial, non-specific protection against infections or pathogens other than the one from which the vaccine is derived. This is the concept of innate immune memory or " trained immunity", which differs from adaptive memory in its non-specificity. Innate immune memory is triggered by exposure to immunostimulants, and offers protection against unrelated pathogenic threats for several months or even years.

The project aims to carry out an exploratory study to observe, in the context of current practice, the immune response obtained after a subunit and a live attenuated vaccine

Vaccine protection depends on a specific adaptive immune memory. However, a little-explored aspect of certain live vaccines may provide beneficial, non-specific protection against infections or pathogens other than the one from which the vaccine is derived. This is the concept of innate immune memory or " trained immunity", which differs from adaptive memory in its non-specificity. Innate immune memory is triggered by exposure to immunostimulants, and offers protection against unrelated pathogenic threats for several months or even years.

For example, research has shown that the live attenuated BCG vaccine induce non-specific trained immunity, enabling innate immune cells to remember their first encounter and improve their immune status during a second confrontation with similar or different agents.

Other currently available live vaccines, such as BCG , could also "train" innate immune cells.

The project aims to carry out an exploratory study to observe, in the context of current practice, the immune response obtained after a subunit and a live attenuated vaccine

Inclusion Criteria:

• Age between 18 and 65
• Referred for immunisation against yellow fever and typhoid
• Any person with indication for the following vaccinations :
• Yellow fever
• Typhoïd
• Whose vaccination schedule includes two appointments 7 days apart
• Whose state of health is compatible with a single 51 ml blood sample collection
• Have consented to participate in the Ivory2 study
• Benefiting from a Social Security plan or equivalent

Exclusion Criteria:

• Anyone with a contraindication to yellow fever and/or typhoid vaccination.
• Any person who has been vaccinated against yellow fever and/or typhoid.
• Anyone who has lived in an endemic area (≥ 1 year) and/or has a history of Typhoid.
• Anyone who is unable to attend the visit 1-month after the typhoid vaccine injection.
• Women claiming to be pregnant or breast-feeding
• Anyone unable to give informed consent for participation