Peer-reviewed article
COVID-19 vaccine effectiveness and duration of protection among children and adolescents: A retrospective cohort study in 11 large cities in Japan.
Kitamura N, Tomo Y, Okuyama M, Ueda K, Matsuoka H et al. ·
Summary
Written by AI, not yet AICS's view · claude-haiku-4-5-20251001This study measured how well COVID-19 vaccines protected children and adolescents aged 5-17 years in Japan against the Omicron variant. The original vaccine provided very little protection against infection but moderate protection against severe disease. Protection from vaccination wore off quickly over time, especially against infection, but protection against severe illness lasted longer. Updated vaccines, particularly the bivalent booster, provided stronger protection against severe disease.
Key points
- Primary series monovalent vaccine showed only 2% effectiveness against any Omicron BA.5 infection in children aged 12-17 years (median 9.6 months after vaccination)
- Bivalent first booster dose showed 41% effectiveness against any infection and 73% effectiveness against severe infection in the 12-17 age group
- Vaccine-derived protection against infection declined to nearly 0% within 10 months after primary series vaccination
- Protection against severe disease persisted longer than protection against infection
- Hybrid immunity (vaccination plus prior infection) provided 83-97% protection
Limitations
The study only assessed protection against the Omicron BA.5 variant and cannot determine effectiveness against other variants or newer strains. The analysis focused on Japanese urban populations in 11 cities, which may not represent rural areas or other geographic regions.
Abstract
Introduction COVID-19 vaccination for children has been debatable. Compiling scientific evidence on vaccine safety and effectiveness was indispensable for the effective vaccine strategy. This study aimed to estimate the effectiveness and protection duration of the COVID-19 vaccine among children and adolescents in Japan. Material and methods A retrospective cohort study was conducted targeting residents aged 5-17 years in 11 cities in Japan. Combining the national SARS-CoV-2 surveillance record and vaccination registry, Cox proportional hazard regression analyses were performed to estimate the effectiveness of the original monovalent vaccine against Omicron infection compared with unvaccinated. The duration of protection was also estimated. Findings A total of 1,908,012 records were included. The effectiveness of primary series vaccination, the monovalent and bivalent first booster dose vaccination against any infection with Omicron BA.5 was 2 % (95 % CI: 0-3 %) (median 9.6 months after vaccination), 39 % (38-40 %), and 41 % (39-44 %) among those aged 12-17 years, respectively. The effectiveness against severe infection with the Omicron BA.5 was 49 % (35-60 %), 54 % (39-65 %), and 73 % (46-87 %), respectively. The result was similar for children aged 5-11 years. The protection of hybrid immunity was estimated at 83-97 %. The vaccine-derived protection waned to nearly 0 % at ten months after primary series vaccination; however, the protection against severe infection persists more than that. Discussion The monovalent vaccine's protection against Omicron infections was limited, partly due to the rapid waning of vaccine-derived immunity. The protection against severe diseases was moderate, especially when the bivalent vaccine was used. The results reassure the importance of updated vaccination.
Findings the Hub has extracted
Each claim below is labelled by its type of design and links back to this report.
- Intervention
- COVID-19 vaccination with original monovalent vaccine, monovalent booster, and bivalent booster doses
- Population
- Children and adolescents aged 5-17 years residing in 11 large cities in Japan (1,908,012 records included)
Key finding
Monovalent primary series vaccine effectiveness against Omicron BA.5 infection: 2% (95% CI: 0-3%) at median 9.6 months