Table 2. Immunogenicity of the mRNA-1273 Vaccine in Part 2 of the Trial.*.
| Variable | Children, 6–11 Yr mRNA-1273, 50 μg (N=320) |
Young Adults, 18–25 Yr mRNA-1273, 100 μg (N=295) |
Children vs. Young Adults |
|---|---|---|---|
| Baseline | |||
| No. of participants with nonmissing data | 317 | 295 | |
| Geometric mean pseudovirus neutralizing antibody titer (95% CI)† | 9.3 (NE to NE) | 9.3 (9.2 to 9.4) | |
| Day 57 | |||
| No. of participants with nonmissing data | 319 | 295 | |
| Geometric mean pseudovirus neutralizing antibody titer (95% CI)‡ | 1610 (1457 to 1780) | 1300 (1171 to 1443) | Geometric mean titer ratio, 1.2 (95% CI, 1.1 to 1.4)‡ |
| Serologic response | |||
| No. of participants/total no. (%)§ | 313/316 (99.1) | 292/295 (99.0) | 0.1 percentage points (95% CI, −1.9 to 2.1)¶ |
| 95% CI‖ | 97.3 to 99.8 | 97.1 to 99.8 |
The 50% inhibitory dilution titer of neutralizing antibodies was determined for participants in the immunogenicity population. For neutralizing antibody values that were assessed by pseudovirus neutralizing antibody assay and reported as being below the lower limit of quantitation (18.5), 0.5 times the lower limit of quantitation was used in the analysis. For values greater than the upper limit of quantitation (45,118), the upper limit of quantitation was used in the analysis if actual values were not available. The young adults group includes participants who were 18 to 25 years of age in the mRNA-1273 group in the COVE trial. The upper limit of quantitation was different for selected COVE trial participants who had undergone testing previously. The data-cutoff date was November 10, 2021. To convert the values for geometric mean pseudovirus neutralizing antibody titers to international units, multiply by 0.242.
The 95% confidence intervals were calculated with the use of t-distribution of the log-transformed values for geometric mean titer (observed or model-based, which is estimated by geometric least-squares means), respectively, then back-transformed to the original scale for presentation.
The log-transformed antibody levels were analyzed with the use of an analysis of covariance model (primary approach) with the group variable (children and young adults in the COVE trial) as a fixed effect. The resulting least-squares means, the difference of least-squares means, and 95% confidence intervals were back-transformed to the original scale for presentation.
The serologic response in participants was defined as an increase in antibody titers from below the lower limit of quantitation to titers that were at least 4 times the lower limit of quantitation, or at least 4 times as high as the baseline value if the baseline titers were equal to or above the lower limit of quantitation. Percentages were based on the number of participants with nonmissing data at baseline and the corresponding time point.
The 95% confidence interval was calculated with the use of the confidence limits in the Miettinen–Nurminen method.
The 95% confidence interval was calculated with the use of the Clopper–Pearson method.