A Study to Evaluate the Safety and Immunogenicity of mRNA-1975 and mRNA-1982 Against Lyme Disease in Participants 18 Through 70 Years of Age

Solicited ARs were collected in an electronic diary (eDiary). Local ARs: injection site pain, erythema (redness), swelling/induration (hardness); and axillary (underarm) swelling or tenderness ipsilateral to the side of injection. Systemic ARs: fever, headache, fatigue, myalgia, arthralgia, nausea/vomiting, and chills. Note, not all solicited ARs were considered adverse events (AEs). Investigator reviewed whether the solicited AR was also to be recorded as an AE. A summary of serious AEs (SAEs) and nonserious AEs ("Other"), regardless of causality, is located in the "Reported Adverse Events" section.

Solicited ARs were collected in an eDiary. Local ARs: injection site pain, erythema (redness), swelling/induration (hardness); and axillary (underarm) swelling or tenderness ipsilateral to the side of injection. Systemic ARs: fever, headache, fatigue, myalgia, arthralgia, nausea/vomiting, and chills. Note, not all solicited ARs were considered AEs. Investigator reviewed whether the solicited AR was also to be recorded as an AE. A summary of SAEs and nonserious AEs ("Other"), regardless of causality, is located in the "Reported Adverse Events" section.

Solicited ARs were collected in an eDiary. Local ARs: injection site pain, erythema (redness), swelling/induration (hardness); and axillary (underarm) swelling or tenderness ipsilateral to the side of injection. Systemic ARs: fever, headache, fatigue, myalgia, arthralgia, nausea/vomiting, and chills. Note, not all solicited ARs were considered AEs. Investigator reviewed whether the solicited AR was also to be recorded as an AE. A summary of SAEs and nonserious AEs ("Other"), regardless of causality, is located in the "Reported Adverse Events" section.

An AE was defined as any untoward medical occurrence associated with the use of a drug in humans, whether or not considered drug related. Any abnormal laboratory test result (hematology, clinical chemistry, or prothrombin time [PT]/partial thromboplastin time [PTT]) or other safety assessment (for example, electrocardiogram, radiological scan, vital sign measurement), including one that worsened from baseline and was considered clinically significant in the medical and scientific judgment of the Investigator was recorded as an AE. A summary of SAEs and all nonserious AEs ("Other"), regardless of causality, is located in the "Reported Adverse Events" section.

A MAAE is an AE that led to an unscheduled visit to a healthcare practitioner. An SAE was defined as any AE that resulted in death, was life-threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in disability, was a congenital anomaly/birth defect, or was an important medical event. An AESI was an AE (serious or nonserious) of scientific and medical concern specific to the Sponsor's product or program, for which ongoing monitoring and immediate notification by the Investigator to the Sponsor were required. A summary of SAEs and all nonserious AEs ("Other"), regardless of causality, is located in the "Reported Adverse Events" section.

Antibody values reported as below lower limit of quantification (LLOQ) were replaced by 0.5*LLOQ. Values reported greater than upper limit of quantification (ULOQ) were replaced by the ULOQ. LLOQ was 41.4 nanograms (ng)/milliliter (mL) and ULOQ was 428000 ng/mL for manual assay; LLOQ was 47.6 ng/mL and 583000 ng/mL for automated assay for SR-1 IgG antibody. 95% confidence interval (CI) for GM value was calculated based on the t-distribution of the log-transformed values , then back transformed to the original scale for presentation.

Antibody values reported as below LLOQ were replaced by 0.5*LLOQ. Values reported greater than ULOQ were replaced by the ULOQ. LLOQ was 30 ng/mL and ULOQ was 214000 ng/mL for manual assay; LLOQ was 66.6 ng/mL and 215000 ng/mL for automated assay for SR-2 IgG antibody. 95% CI for GM value was calculated based on the t-distribution of the log-transformed values, then back transformed to the original scale for presentation. Since mRNA-1982 was designed to elicit antibodies against SR-1 antigen only, the data for this outcome measure has been reported for mRNA-1975 and placebo arms only.

Antibody values reported as below LLOQ were replaced by 0.5*LLOQ. Values reported greater than ULOQ were replaced by the ULOQ. LLOQ was 14.5 ng/mL and ULOQ was 299000 ng/mL for manual assay; LLOQ was 62.5 ng/mL and 296000 ng/mL for automated assay for SR-3 IgG antibody. 95% CI for GM value was calculated based on the t-distribution of the log-transformed values, then back transformed to the original scale for presentation. Since mRNA-1982 was designed to elicit antibodies against SR-1 antigen only, the data for this outcome measure has been reported for mRNA-1975 and placebo arms only.

Antibody values reported as below LLOQ were replaced by 0.5*LLOQ. Values reported greater than ULOQ were replaced by the ULOQ. LLOQ was 32.6 ng/mL and ULOQ was 292000 ng/mL for manual assay; LLOQ was 59.7 ng/mL and 264000 ng/mL for automated assay for SR-4 IgG antibody. 95% CI for GM value was calculated based on the t-distribution of the log-transformed values, then back transformed to the original scale for presentation. Since mRNA-1982 was designed to elicit antibodies against SR-1 antigen only, the data for this outcome measure has been reported for mRNA-1975 and placebo arms only.

Antibody values reported as below LLOQ were replaced by 0.5*LLOQ. Values reported greater than ULOQ were replaced by the ULOQ. LLOQ was 45.5 ng/mL and ULOQ was 298000 ng/mL for manual assay; LLOQ was 84.2 ng/mL and 319000 ng/mL for automated assay for SR-5 IgG antibody. 95% CI for GM value was calculated based on the t-distribution of the log-transformed values, then back transformed to the original scale for presentation. Since mRNA-1982 was designed to elicit antibodies against SR-1 antigen only, the data for this outcome measure has been reported for mRNA-1975 and placebo arms only.

Antibody values reported as below LLOQ were replaced by 0.5*LLOQ. Values reported greater than ULOQ were replaced by the ULOQ. LLOQ was 18.1 ng/mL and ULOQ was 203000 ng/mL for manual assay; LLOQ was 68.7 ng/mL and 248000 ng/mL for automated assay for SR-6 IgG antibody. 95% CI for GM value was calculated based on the t-distribution of the log-transformed values, then back transformed to the original scale for presentation. Since mRNA-1982 was designed to elicit antibodies against SR-1 antigen only, the data for this outcome measure has been reported for mRNA-1975 and placebo arms only.

Antibody values reported as below LLOQ were replaced by 0.5*LLOQ. Values reported greater than ULOQ were replaced by the ULOQ. LLOQ was 13 ng/mL and ULOQ was 197000 ng/mL for manual assay; LLOQ was 78.9 ng/mL and 174000 ng/mL for automated assay for SR-7 IgG antibody. 95% CI for GM value was calculated based on the t-distribution of the log-transformed values, then back transformed to the original scale for presentation. Since mRNA-1982 was designed to elicit antibodies against SR-1 antigen only, the data for this outcome measure has been reported for mRNA-1975 and placebo arms only.

Antibody values reported as below LLOQ were replaced by 0.5*LLOQ. Values reported greater than ULOQ were replaced by the ULOQ. LLOQ was 41.4 ng/mL and ULOQ was 428000 ng/mL for manual assay; LLOQ was 47.6 ng/mL and 583000 ng/mL for automated assay for SR-1 IgG antibody. 95% CI for GMFR value was calculated based on the t-distribution of the difference in the log-transformed values, then back transformed to the original scale for presentation.

Antibody values reported as below LLOQ were replaced by 0.5*LLOQ. Values reported greater than ULOQ were replaced by the ULOQ. LLOQ was 30 ng/mL and ULOQ was 214000 ng/mL for manual assay; LLOQ was 66.6 ng/mL and 215000 ng/mL for automated assay for SR-2 IgG antibody. 95% CI for GMFR value was calculated based on the t-distribution of the difference in the log-transformed values, then back transformed to the original scale for presentation. Since mRNA-1982 was designed to elicit antibodies against SR-1 antigen only, the data for this outcome measure has been reported for mRNA-1975 and placebo arms only.

Antibody values reported as below LLOQ were replaced by 0.5*LLOQ. Values reported greater than ULOQ were replaced by the ULOQ. LLOQ was 14.5 ng/mL and ULOQ was 299000 ng/mL for manual assay; LLOQ was 62.5 ng/mL and 296000 ng/mL for automated assay for SR-3 IgG antibody. 95% CI for GMFR value was calculated based on the t-distribution of the difference in the log-transformed values, then back transformed to the original scale for presentation. Since mRNA-1982 was designed to elicit antibodies against SR-1 antigen only, the data for this outcome measure has been reported for mRNA-1975 and placebo arms only.

Antibody values reported as below LLOQ were replaced by 0.5*LLOQ. Values reported greater than ULOQ were replaced by the ULOQ. LLOQ was 32.6 ng/mL and ULOQ was 292000 ng/mL for manual assay; LLOQ was 59.7 ng/mL and 264000 ng/mL for automated assay for SR-4 IgG antibody. 95% CI for GMFR value was calculated based on the t-distribution of the difference in the log-transformed values, then back transformed to the original scale for presentation. Since mRNA-1982 was designed to elicit antibodies against SR-1 antigen only, the data for this outcome measure has been reported for mRNA-1975 and placebo arms only.

Antibody values reported as below LLOQ were replaced by 0.5*LLOQ. Values reported greater than ULOQ were replaced by the ULOQ. LLOQ was 45.5 ng/mL and ULOQ was 298000 ng/mL for manual assay; LLOQ was 84.2 ng/mL and 319000 ng/mL for automated assay for SR-5 IgG antibody. 95% CI for GMFR value was calculated based on the t-distribution of the difference in the log-transformed values, then back transformed to the original scale for presentation. Since mRNA-1982 was designed to elicit antibodies against SR-1 antigen only, the data for this outcome measure has been reported for mRNA-1975 and placebo arms only.

Antibody values reported as below LLOQ were replaced by 0.5*LLOQ. Values reported greater than ULOQ were replaced by the ULOQ. LLOQ was 18.1 ng/mL and ULOQ was 203000 ng/mL for manual assay; LLOQ was 68.7 ng/mL and 248000 ng/mL for automated assay for SR-6 IgG antibody. 95% CI for GMFR value was calculated based on the t-distribution of the difference in the log-transformed values, then back transformed to the original scale for presentation. Since mRNA-1982 was designed to elicit antibodies against SR-1 antigen only, the data for this outcome measure has been reported for mRNA-1975 and placebo arms only.

Antibody values reported as below LLOQ were replaced by 0.5*LLOQ. Values reported greater than ULOQ were replaced by the ULOQ. LLOQ was 13 ng/mL and ULOQ was 197000 ng/mL for manual assay; LLOQ was 78.9 ng/mL and 174000 ng/mL for automated assay for SR-7 IgG antibody. 95% CI for GMFR value was calculated based on the t-distribution of the difference in the log-transformed values, then back transformed to the original scale for presentation. Since mRNA-1982 was designed to elicit antibodies against SR-1 antigen only, the data for this outcome measure has been reported for mRNA-1975 and placebo arms only.

A death that occurred during the study or that came to the attention of the investigator during the study was reported to the Sponsor, whether or not it was considered related to study drug. The investigator assessed causality (that is, whether there is a reasonable possibility that the study drug caused the death). The relationship was characterized using the following classifications: Not related: There was not a reasonable possibility of a relationship to the study drug. The temporal sequence of the death relative to administration of the study drug was not reasonable AND/OR the death was more likely explained by a cause other than the study drug. Related: There was a reasonable possibility of a relationship to the study drug. There was evidence of exposure to the study drug. The temporal sequence of the death relative to the administration of the study drug was reasonable. The death was more likely explained by the study drug than by another cause.