Baseline Assessment of Skin Resident Memory T Cells in Healthy Unvaccinated Participants

In The main GeKoSkimm trial (= A randomized controlled trial to compare the immunogenicity and skin imprinting of intradermal, subcutaneous and intramuscular yellow fever vaccination) the investigators try to understand whether the route of injection (in the muscle, under the skin, or in the skin) when giving the yellow fever vaccine affects the strength of the body's immune response to yellow fever. More in particular the investigators want to know how well the immune responses are retained in the skin, as this is the place where the virus enters the body after a mosquito bite. This will be important for vaccines against infections transmitted via bites of mosquitoes and ticks, such as yellow fever virus. Because this is the first attempt on human samples and only skin samples after vaccination with yellow fever vaccine are available, the investigators want to assess the baseline or background immune response in 'unvaccinated' skin. Therefore, 40 volunteers will be recruited that have not been previously vaccinated against yellow fever and will not receive a yellow fever vaccine during this study. The participant will be requested to provide two skin samples from the upper arm and a blood sample to confirm their vaccination status regarded to yellow fever.