Covid-19 Vaccine Protection among Children and Adolescents in Qatar

Abstract

Background: The BNT162b2 vaccine against coronavirus disease 2019 (Covid-19) has been authorized for use in children 5 to 11 years of age and adolescents 12 to 17 years of age but in different antigen doses.

Methods: We assessed the real-world effectiveness of the BNT162b2 vaccine against infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) among children and adolescents in Qatar. To compare the incidence of SARS-CoV-2 infection in the national cohort of vaccinated participants with the incidence in the national cohort of unvaccinated participants, we conducted three matched, retrospective, target-trial, cohort studies - one assessing data obtained from children 5 to 11 years of age after the B.1.1.529 (omicron) variant became prevalent and two assessing data from adolescents 12 to 17 years of age before the emergence of the omicron variant (pre-omicron study) and after the omicron variant became prevalent. Associations were estimated with the use of Cox proportional-hazards regression models.

Results: Among children, the overall effectiveness of the 10-μg primary vaccine series against infection with the omicron variant was 25.7% (95% confidence interval [CI], 10.0 to 38.6). Effectiveness was highest (49.6%; 95% CI, 28.5 to 64.5) right after receipt of the second dose but waned rapidly thereafter and was negligible after 3 months. Effectiveness was 46.3% (95% CI, 21.5 to 63.3) among children 5 to 7 years of age and 16.6% (95% CI, -4.2 to 33.2) among those 8 to 11 years of age. Among adolescents, the overall effectiveness of the 30-μg primary vaccine series against infection with the omicron variant was 30.6% (95% CI, 26.9 to 34.1), but many adolescents had been vaccinated months earlier. Effectiveness waned over time since receipt of the second dose. Effectiveness was 35.6% (95% CI, 31.2 to 39.6) among adolescents 12 to 14 years of age and 20.9% (95% CI, 13.8 to 27.4) among those 15 to 17 years of age. In the pre-omicron study, the overall effectiveness of the 30-μg primary vaccine series against SARS-CoV-2 infection among adolescents was 87.6% (95% CI, 84.0 to 90.4) and waned relatively slowly after receipt of the second dose.

Conclusions: Vaccination in children was associated with modest, rapidly waning protection against omicron infection. Vaccination in adolescents was associated with stronger, more durable protection, perhaps because of the larger antigen dose. (Funded by Weill Cornell Medicine-Qatar and others.).

Figure 1. Omicron Infection in Children 5 to 11 Years of Age, According to Vaccination Status, and Effectiveness of the 10-μg Vaccine Dose.

Panel A shows the cumulative incidence of infection with the B.1.1.529 (omicron) variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) among children 5 to 11 years of age who had received two 10-μg doses of the BNT162b2 vaccine, as compared with unvaccinated children (control). The inset shows the same data on an expanded y axis. Panel B shows the vaccine effectiveness against omicron infection among children who had received two 10-μg doses according to the number of months after the start of follow-up. Follow-up began 14 days after receipt of the second dose. The lower boundary of the 95% confidence interval (𝙸 bar) for the data at month 4 or later has been truncated.

Figure 2. SARS-CoV-2 Infection in Adolescents 12 to 17 Years of Age, According to Vaccination Status, in the Pre-Omicron and Omicron Studies.

Shown is the cumulative incidence of SARS-CoV-2 infection among adolescents 12 to 17 years of age who had received two 30-μg doses of the BNT162b2 vaccine, as compared with unvaccinated adolescents (control) in studies assessing data during the period before the omicron variant became prevalent (pre-omicron study, Panel A) and after the omicron variant became prevalent (omicron study, Panel B). In both panels, the inset shows the same data on an enlarged y axis.

Figure 3. Effectiveness of the 30-μg Vaccine Dose in Adolescents 12 to 17 Years of Age before and after the Emergence of the Omicron Variant.

Panel A shows the effectiveness of the 30-μg dose of BNT162b2 vaccine against SARS-CoV-2 infection before the emergence of the omicron variant (pre-omicron study) among adolescents according to the number of months after receipt of the second dose. Follow-up began 14 days after receipt of the second dose. The lower boundary of the 95% confidence interval (𝙸 bar) for the data at month 4 has been truncated. Panel B shows the effectiveness of the 30-μg dose against omicron infection among adolescents according to date of receipt of the second dose. The date groups are shown in the order of increasing time since receipt of the second dose. 𝙸 bars indicate 95% confidence intervals.