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Amidst the ongoing battle against the evolving SARS-CoV-2 virus, a recent study published by Annals of Internal Medicine suggests that the BNT162b2 vaccine was effective for various COVID–19–related outcomes in children and adolescents during the Delta and Omicron periods. Researchers observed evidence of waning effectiveness over time. This study is the first real-world effectiveness evaluation of COVID-19 vaccines against infection and severe outcomes, explicitly addressing underreporting in vaccination.
During the Delta period, the BNT162b2 vaccine showed an estimated effectiveness of 98.4% (95% CI, 98.1% to 98.7%) against documented infection among adolescents. During the Omicron period, the effectiveness against documented infection was estimated to be 74.3% (CI, 72.2% to 76.2%) among children and 85.5% (CI, 83.8% to 87.1%) among adolescents. Four months after the first dose, vaccine effectiveness against documented Omicron infection declined from 82.3% to 70.6% for children and from 91.3% to 82.9% for adolescents. The study consisted of 77, 392 adolescents, 44,007 vaccinated during the Delta phase and 111, 539 children, 50,398 vaccinated, and 56,080 adolescents 21,180 vaccinated, during the Omicron phase.
“Our study has several strengths. First, we used a national network of academic medical centers that covered a diverse cohort being more representative of the general pediatric population, provided a robust sample size, and allowed for multiple subgroup analyses and detection of rare outcomes.” Investigators wrote. “Second, the richness of these HER (Electronic Health Record System) data allowed us to investigate the effectiveness against infection of different levels of severity as well as adjust for a broad set of confounders. Third, we conducted the negative control outcome experiments to assess the potential residual bias due to unmeasured confounders and other potential sources of systematic bias in the data.”1
According to the study, during the dominant period of the Delta variant, an analysis of cardiac complications did not suggest a statistically significant difference between vaccinated and unvaccinated groups.
“During the period when the Delta variant was dominant, the BNT162b2 vaccine was associated with strong protection in adolescents, with effectiveness higher than 95%, and with little evidence of waning during the follow-up period,” the investigators wrote. “Our findings against the Delta infection among adolescents are consistent with vaccine efficacy seen in the BNT162b2 clinical trial involving adolescents aged between 12 and 15 years, which demonstrated vaccine efficacy of 100% (CI, 75.3% to 100%) against documented SARS-CoV-2 infection.”1
During the prevalent period of the Omicron variant, the analysis showed a lower risk for cardiac complications in the vaccinated group during the Omicron variant period. Among adolescents, the effectiveness against documented Omicron infection was 84.8% (CI, 77.3% to 89.9%) against moderate or severe COVID-19 and 91.5% (CI, 69.5% to 97,6%) against ICU admission with COVID-19. The protection decreased by approximately 10% around 4 months after the first dose, then stabilized exhibiting a slight waning trend over time.
3 Key Takeaways
This research is highlighted as the first real-world effectiveness evaluation of COVID-19 vaccines against infection and severe outcomes in children and adolescents.
The study states during the Delta variant period, the vaccine demonstrated strong protection with an estimated effectiveness exceeding 95%, and there was little evidence of waning effectiveness during the follow-up period.
The effectiveness against documented Omicron infection showed a decline around four months after the first dose, stabilizing with a slight waning trend over time.
Based on the researchers’ studies from different regions, such as Scotland and the United States, indicated varying vaccine effectiveness against Omicron infection among different age groups, demonstrating effectiveness levels ranging from 20% to 82%. Notably, the effectiveness was found to be substantially lower against later subvariants of Omicron, such as BQ.1 and XBB, prompting the need for ongoing research to comprehend the vaccine's effectiveness on future subvariants and potential waning effects.
In conclusion, the study highlights the effectiveness of BNT162b2 in preventing infection and severe disease with various strains of the SARS-CoV-2 virus in previously uninfected children and adolescents. The findings guide the ongoing development of vaccination strategies. The findings also emphasize the need for ongoing research to understand the vaccine's effectiveness on future subvariants and potential waning effects, reflecting the dynamic nature of the COVID-19 pandemic.
Wu Q, Tong J, Zhang B, et al. Real-World Effectiveness of BNT162b2 Against Infection and Severe Diseases in Children and Adolescents. Ann Intern Med. Published online January 9, 2024. doi:10.7326/M23-1754