This is a Phase 1, single-site, open-label, comparator-controlled dose escalating study of an intramuscularly (IM) administered mRNA-LNP vaccine encoding for (Vaccine Research Center) VRC H1ssF 3928 of up to 50 healthy adult volunteers aged 18 to 49 years, inclusive. This study is designed to assess the safety and immunogenicity of one dose of H1ssF 3928 mRNA Vaccine. Eligible participants will be sequentially enrolled into dosing groups (10 mcg, 25 mcg, and 50 mcg, selected optimal dose) to receive the H1ssF 3928 mRNA Vaccine at the specified dose. A separate group of 10 participants will receive licensed quadrivalent influenza vaccine (IIV4). Subjects receiving IIV4 will be followed for safety but only their immune responses will be compared to those of participants receiving H1ssF 3928 mRNA Vaccine. Dosing of H1ssF 3928 mRNA Vaccine will commence at the lowest dose (10 mcg) and only escalate to the next highest dose if safety concerns are not identified. For each VRC H1ssF 3928 mRNA-LNP (Lipid Nanoparticle) dosing group, the first two subjects enrolled will be considered the sentinel subgroup. After the two subjects in the Low Dose sentinel subgroup are enrolled and given their vaccination, enrollment will then be stopped pending a review of the reactogenicity and safety data collected through Day 3 for both subjects. Approval by the reviewing group will allow for continued enrollment of the remaining Low Dose Group subjects to complete enrollment of 10 participants. After Low Dose Group enrollment is completed, enrollment will be stopped pending an Safety Review Committee (SRC) review of the reactogenicity and adverse event (AE) information through Day 7 and clinical laboratory results through Day 8 for all Low Dose Group subjects. Approval will allow dose escalation and initiation of enrollment of the Medium Dose Group sentinel subgroup. After the two subjects in the Medium Dose sentinel subgroup are enrolled and given their vaccination, enrollment will then be stopped pending a safety review of the sentinel subgroup as specified for the Low Dose Group. Approval will allow for continued enrollment of Medium Dose Group subjects to complete enrollment of 10 participants. After the Medium Dose Group enrollment is completed, enrollment will be stopped pending an SRC review of the reactogenicity and adverse event information through Day 7 and clinical laboratory results through Day 8 for all Medium Dose Group subjects. Approval will allow dose escalation and initiation of enrollment of the High Dose Group sentinel subgroup. After the two subjects in the High Dose sentinel subgroup are enrolled and given their vaccination, enrollment will then be stopped pending a safety review of the sentinel subgroup as specified for the Low and Medium Dose Groups. Approval will allow for continued enrollment of High Dose Group subjects to complete enrollment of 10 participants. After the High Dose Group enrollment is completed, enrollment will be stopped pending an SRC review of the reactogenicity and adverse event information through Day 7 visit and clinical laboratory results through Day 8 for all High Dose Group subjects. Reactogenicity and AE information through Day 7 and clinical laboratory results through Day 8 from the first three dosing groups will guide the selection of an optimal dose group to include an additional 10 subjects who will receive the optimal dose of mRNA-LNP. The primary objective of this study is to assess the safety of a single dose of VRC H1ssF 3928 mRNA-LNP vaccine administered IM in healthy adults, 18-49 yrs, at doses of 10 mcg, 25 mcg, and 50 mcg. The secondary objective of this study is to assess serum antibody responses to a single dose of VRC H1ssF 3928 mRNA-LNP vaccine administered IM in healthy adults at doses of 10 mcg, 25 mcg, and 50 mcg in comparison to a standard dose of IIV4.