Table 2. Results of Serum SARS-CoV-2 Neutralization Assay for the Ancestral Strain.*.
| Timing of Assay and Age Group | BNT162b2 Dose Level | No. of Participants | Geometric Mean 50% Neutralizing Titer (95% CI)† | Geometric Mean Ratio vs. 16 to 25 Yr of Age (95% CI)‡ | Seroresponse (95% CI)§ | Difference in Seroresponse vs. 16 to 25 Yr of Age (95% CI)¶ |
|---|---|---|---|---|---|---|
| μg | percent | percentage points | ||||
| 1 mo after BNT162b2 dose 3 (6 mo to 4 yr of age) or dose 2 (16 to 25 yr of age) | ||||||
| 6 mo to <2 yr | 3 | 80 to 82 | 1406.5 (1211.3 to 1633.1) |
1.19 (1.00 to 1.42) |
100.0 (95.5 to 100.0) |
1.2 (–3.4 to 4.2) |
| 2 to 4 yr | 3 | 141 to 143 | 1535.2 (1388.2 to 1697.8) |
1.30 (1.13 to 1.50) |
100.0 (97.4 to 100.0) |
1.2 (–1.5 to 4.2) |
| 16 to 25 yr | 30 | 170 | 1180.0 (1066.6 to 1305.4) |
— | 98.8 (95.8 to 99.9) |
— |
| 1 mo after BNT162b2 dose 2 (all age groups) | ||||||
| 6 mo to <2 yr and 16 to 25 yr | ||||||
| 6 mo to <2 yr | 3 | 245 | 979.7 (893.2 to 1074.6) |
1.03 (0.90 to 1.19) |
98.0 (95.3 to 99.3) |
1.7 (–1.4 to 5.2) |
| 16 to 25 yr | 30 | 238 | 946.8 (850.8 to 1053.7) |
— | 96.2 (92.9 to 98.3) |
— |
| 2 to 4 yr and 16 to 25 yr | ||||||
| 2 to 4 yr | 3 | 243 | 763.9 (688.5 to 847.5) |
0.61 (0.53 to 0.70) |
96.7 (93.6 to 98.6) |
–0.9 (–4.3 to 2.3) |
| 16 to 25 yr | 30 | 251 or 252 | 1255.4 (1131.2 to 1393.3) |
— | 97.6 (94.9 to 99.1) |
— |
Results are for the dose 3 and dose 2 immunogenicity population that could be evaluated of the immunobridging subgroup for participants 6 months to 4 years of age and the dose 2 immunogenicity population that could be evaluated for participants 16 to 25 years of age (Table S1) who had no serologic or virologic evidence of past or current SARS-CoV-2 infection up to the visit 1 month after dose 2 (16 to 25 years of age and 6 months to 4 years of age) or the visit 1 month after dose 3 (6 months to 4 years of age) and who had no history of Covid-19. Further details on the dose 3 population that could be evaluated and the timing intervals for dose 3 administration are provided in the Supplementary Appendix. Missing immunogenicity data were not imputed.
Geometric mean titers and two-sided 95% confidence intervals (CIs) were calculated by exponentiation of the mean logarithm of the titers and the corresponding confidence intervals (based on Student’s t distribution). Assay results below the lower limit of quantitation were set to 0.5 times the lower limit of quantitation.
The geometric mean ratio and two-sided 95% confidence intervals were calculated by exponentiation of the mean difference of the logarithms of the titers (children 6 months to <2 years of age minus persons 16 to 25 years of age, and children 2 to 4 years of age minus persons 16 to 25 years of age) and the corresponding confidence intervals (based on Student’s t distribution). The immunobridging criterion was met because the lower boundary of the two-sided confidence interval for the geometric mean ratio was more than 0.67, and the point estimate of the geometric mean ratio was at least 0.8.
Confidence intervals were calculated with the Clopper–Pearson method.
Confidence intervals were calculated with the Miettinen–Nurminen method. Immunobridging success also required a lower boundary of the 95% confidence interval for the difference in percentages of participants (between children 6 months to <2 years of age or those 2 to 4 years of age and persons 16 to 25 years of age) with a seroresponse to be greater than −10 percentage points.