The right arm has been specifically selected as lymphatics in the right upper part of the body drains directly into the blood stream via the right lymphatic duct with no shared lymphatic connections to the rest of the body. In contrast lymph from the rest of the body ultimately drains into the thoracic duct (see figure below). By immunising the right arm the investigators can be sure that vaccine antigens and antigen presenting cells and activated lymphocytes will not pass through any lymph nodes in common with the cervix or vagina. In contrast by injecting the anterolateral thigh (right side selected for uniformity) the investigators can be sure that vaccine antigens will pass through the external inguinal lymph nodes which will also receive antigens and lymphocytes responding to vaginal or cervical infection or inflammation. The choice of right leg is just to standardise.