Healthy non-pregnant women 18-45 years of age will be randomized in a 1:1:1:1 ratio to receive one of three dose levels (30, 60, 120 micrograms [µg]) of the investigational RSV maternal vaccine (GSK3888550A) or placebo, administered as a single intramuscular injection (IM).~There will be a screening visit and five study visits scheduled at Day 1 (study vaccination), Day 8, Day 31, Day 61, and Day 91 to evaluate the primary and secondary objectives of safety/reactogenicity and immunogenicity profiles of the 3 dose levels. Subjects will also be contacted at Day 181. During this contact, the investigator (or delegate) will ask the subject if she has experienced any serious adverse events (SAEs) and or any adverse events (AEs) leading to study withdrawal since the last study visit (Day 360), as well as if she has become pregnant during the post-vaccination period. The investigator (or delegate) will also ask the subject about concomitant vaccinations/products/medications that she has received since the last study visit (D91). Contact should be performed preferably via telephone. Other means of contact (email/other) may be acceptable provided the required information can be fully collected.
The purpose of this study is to evaluate different dose levels of the investigational RSV maternal vaccine (GSK3888550A) based on safety/reactogenicity and immune response data.~As this is the first time the investigational RSV maternal vaccine (GSK3888550A) is being been used in humans, this study will be performed in healthy non-pregnant women 18-45 years of age before testing in pregnant women.