Yes, it is possible. I know people in my program who have done this and who are doing it this summer. Just keep in mind that the cost of living in Geneva is high and the majority (to my knowledge) of WHO internships are unpaid. Some schools keep a database for students of past internships/practicums that students have done with connections these students have made. This helps us know who we can reach out to and which school faculty members may have assisted. The WHO likely also directly posts internships that you can apply to. Many schools may have some connection to WHO, or have a faculty memeber with a connection, so make sure to express your interest within your program early. Also, it would be helpful to see if your school offers funding for students who do international or unpaid internships. Good luck!