TABLE 3. COVID-19 Pfizer-BioNTech vaccine effectiveness against asymptomatic or symptomatic SARS-CoV-2 infection among children and adolescents aged 5–15 years, by time since receipt of second vaccine dose and variant — PROTECT* cohort study, four states, July 2021–February 2022.
| Age group and COVID-19 vaccination status (no. of days since receipt of most recent dose) | No. of contributing participants† | Total person-days | Median no. of days (IQR) | No. of SARS-CoV-2 infections§ | VE, % (95% CI) |
|
|---|---|---|---|---|---|---|
| Unadjusted | Adjusted¶ | |||||
|
Children aged 5–11 yrs
| ||||||
|
Omicron variant infections
| ||||||
| Unvaccinated (referent) |
336 |
13,801 |
41 (28 to 62) |
137 |
— |
— |
| 2 doses (14–82 days) |
640 |
29,996 |
53 (34 to 61) |
184 |
47 (32 to 59) |
31 (9 to 48) |
|
Adolescents aged 12–15 yrs
| ||||||
|
Delta variant infections
| ||||||
| Unvaccinated (referent) |
139 |
9,786 |
65 (25 to 107) |
23 |
— |
— |
| 2 doses (≥14 days) |
193 |
23,575 |
142 (91 to 156) |
7 |
87 (70 to 95) |
81 (51 to 93) |
| 2 doses (14–149 days) |
188 |
16,517 |
97 (75 to 105) |
3 |
93 (76 to 98) |
87 (49 to 97) |
| 2 doses (≥150 days) |
138 |
7,058 |
57 (49 to 63) |
4 |
67 (0 to 89) |
60 (−35 to 88) |
|
Omicron variant infections
| ||||||
| Unvaccinated (referent) |
76 |
3,001 |
37 (24 to 62) |
38 |
— |
— |
| 2 doses (≥14 days) |
192 |
5,432 |
22 (22 to 31) |
18 |
64 (37 to 80) |
59 (24 to 78) |
| 2 doses (14–149 days) |
65 |
2,623 |
42 (28 to 56) |
14 |
62 (30 to 79) |
59 (22 to 79) |
| 2 doses (≥150 days) | 134 | 2,809 | 22 (22 to 22) | 4 | 74 (16 to 92) | 62 (−28 to 89) |
Abbreviations: SMD = standard mean difference; VE = vaccine effectiveness.
* PROTECT (Pediatric Research Observing Trends and Exposures in COVID-19 Timelines) is conducted in Phoenix and Tucson, Arizona; Miami, Florida; Temple, Texas; and Salt Lake City, Utah.
† Vaccination status varied with time, therefore, contributing participants in vaccination categories do not equal the number of participants in the study because participants could contribute to more than one vaccination category.
§ Of 275 SARS-CoV-2 infections among unvaccinated participants, 98 occurred among children aged 5–11 years either before vaccine availability (n = 60) or were Delta infections (n = 17) for whom VE was not calculated. Among vaccinated participants, 61 occurred after receipt of dose 1 and <14 days after dose 2; two children aged 5–11 years were vaccinated before authorization, and two had Delta infections among children aged 5–11 years for whom VE was not calculated.
¶ Adjusted VE is inversely weighted for propensity to be vaccinated. Among children aged 5–11 years, all covariates met balance criteria of SMD <0.2 after weighting for the Delta variant model. For the Omicron variant model, all covariates met balance criteria of SMD <0.2 after weighting, except local virus circulation and social (school or community) mask use, which both changed the VE estimate by ≥5% when added to the model, and thus remained in the final model as covariates. Among adolescents aged 12–15 years, all covariates met balance criteria of SMD <0.2 after weighting except social mask use, which also changed the VE estimate by ≥5% when added to the Delta variant model, and thus remained in the final model as a covariate. For the Omicron variant model, all covariates met balance criteria of SMD <0.2 after weighting, except local virus circulation, social (school or community) mask use, and number of medications. Only local virus circulation changed the VE estimate by ≥5% when added to the model, and thus remained in the final model as a covariate.