Peer-reviewed article
Effectiveness of the COVID-19 messenger RNA vaccine against symptomatic omicron infection in children aged 6 months to 11 years in Japan.
Yuta Aizawa, Yugo Shobugawa, Jun Tachikawa, Tatsuki Ikuse, Chansu Shin et al. ·
Summary
Written by AI, not yet AICS's view · claude-haiku-4-5-20251001This study evaluated how well COVID-19 messenger RNA vaccines protect children aged 6 months to 11 years against symptomatic omicron infection in Japan. Researchers compared children who tested positive for COVID-19 with those who tested negative, tracking vaccination status and timing. The vaccine provided strong protection in the first three months after the last dose, but protection declined over time, especially after six months. Protection was strongest in children who had not previously had COVID-19.
Key points
- In children aged 6 months to 4 years, vaccine effectiveness was 73% within 3 months of the last dose, 64% at 3-6 months, and 46% at 6+ months after vaccination
- In children aged 5-11 years who received 2 or more doses, vaccine effectiveness was 59% within 3 months, 57% at 3-6 months, and negative 13% at 6+ months
- Protection was statistically significant only among children without a prior history of COVID-19 infection
- The study tracked two omicron outbreak waves dominated by different subvariants (XBB/EG.5 and BA.2.86/JN.1)
- Study included 516 cases and 2,939 controls for younger children, and 723 cases and 2,745 controls for older children
Limitations
The study is observational and cannot establish causation as definitively as a randomized trial. The findings apply specifically to omicron variants in Japan and may not generalize to other variants or populations in different regions.
Abstract
BACKGROUND: COVID-19 messenger RNA (mRNA) vaccination coverage among children remains low, especially among children aged 6 months to 4 years. In addition, data on vaccine effectiveness (VE) for this age group are limited. METHODS: A prospective, test-negative, case-control study was conducted between April 2023 and April 2024 at 9 pediatric clinics in Niigata, Japan. Patients aged 6 months to 11 years with upper respiratory tract symptoms were tested for SARS-CoV-2, and a multivariable logistic regression model was used to calculate VE against symptomatic COVID-19. RESULTS: Two Omicron outbreaks occurred, predominated by subvariants XBBs/EG.5 and BA.2.86/JN.1, respectively. Among children aged 6 months to 4 years, we included 516 cases and 2939 controls. VE was 73% (95% CI, 12-92%) within 3 months after the last vaccine dose, 64% (95% CI, 19-84%) at 3-6 months, and 46% (95% CI, -24% to 76%) at 6 months and later. Among children aged 5 to 11 years, we included 723 cases and 2745 controls and VE for those who received ≥2 doses was 59% (95% CI, 20-79%) within 3 months after the last vaccine dose, 57% (95% CI, 24-76%) at 3-6 months, and - 13% (95% CI, -40% to 9%) at 6 months and later. When stratified by history of COVID-19, statistically significant protection was observed only among children without a history of COVID-19 (at 3-6 months: 6 months to 4 years, VE 70% [95% CI, 21-88%]; 5-11 years, VE 73% [95% CI, 42-87%]). CONCLUSIONS: In children aged 6 months to 4 years, as well as those aged 5-11 years, the COVID-19 mRNA vaccine was effective against symptomatic Omicron infection within 6 months after the last dose.
Findings the Hub has extracted
Each claim below is labelled by its type of design and links back to this report.
- Intervention
- COVID-19 messenger RNA vaccination
- Population
- Children aged 6 months to 11 years in Niigata, Japan, presenting with upper respiratory tract symptoms during April 2023 to April 2024
Key finding
Vaccine effectiveness against symptomatic omicron in 6 months to 4 years: 73% (0-3 months), 64% (3-6 months), 46% (6+ months)