Phase 4 Clinical Trial of Cervico-vaginal Immune Responses Following Three Right Deltoid or Right Thigh Intramuscular Immunisations With TicoVac (Tick Borne Encephalitis Virus [TBEV]) Vaccine in Adult Female Participants

The study will investigate whether targeting vaccine antigens to lymph nodes (internal iliac) which drain both the lower limb and the cervix/vagina alters the subsequent antibody response detected in the cervix/vagina, when compared with targeting vaccine antigens to unrelated lymph nodes such as those in the axilla that drain the right deltoid muscle of upper arm.

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.

It is the investigators hypothesis therefore that as a result of antigen presentation and stimulation within a specifically "genital tract milieu" T &B lymphocytes leaving the external iliac nodes as a result of an immunisation into the thigh will be patterned in such a way as to more likely home back to the cervix and vagina due to the common drainage of the cervix, vagina and thigh (Figure 1) into the external iliac and lateral aortic lymph nodes. In contrast, cells leaving the axillary lymph nodes after immunisation of the right arm will enter the blood directly via the right lymphatic duct and so will not pass through any lymph nodes in common with the cervix and vagina.

The investigators will detect an effect of targeted immunisation in a number of ways:

1. By detecting increased levels of vaccine-specific antibodies in cervico-vaginal secretions as a result of more activated B cells (plasmablasts) homing back to the genital tract. IgG antibodies may be transudated from the blood but local mucosal IgG may also be produced. In contrast, mucosal IgA is most likely to be locally produced and may therefore be preferentially affected by targeted immunisation. However as individual levels of mucosal antibody vary widely between subjects, especially with IgA, the investigators will set primary endpoints on the basis of a fold-increase in antibody levels from baseline, rather than concentration. As mucosal IgG responses are generally more reliable and of greater magnitude the investigators have set the primary objective as vaccine-specific mucosal IgG after all three immunisations. Vaccine-specific mucosal IgA responses after all three immunisations are the secondary objective. The study has been powered on the basis of the investigators limited experience with similar vaccines to detect a doubling of proportions of responders for IgG and IgA. The investigators have based the fold-increase in vaccine-specific mucosal IgG and IgA on the investigators limited experience with a similar vaccine injected into the arm(7).