Rubella immunization policy in Japan: Immunity gaps arising from program differences and inconsistent cutoff...

Area of Science:

• Immunology
• Public Health
• Epidemiology

Background:

• Rubella elimination is a global priority due to congenital rubella syndrome (CRS) risks.
• Japan's vaccination policy evolved from female-only to universal childhood immunization.
• A "lost generation" of men (born 1962-1978) and inconsistent CRS program cutoffs led to outbreaks.

Purpose of the Study:

• To analyze how vaccination program design and inconsistent serological cutoff standards affect apparent immunity.
• To evaluate the impact of Japan's Phase 5 catch-up program and CRS prevention program on rubella immunity.
• To identify lessons for rubella elimination strategies based on Japan's experience.

Main Methods:

• Analysis of single-institution data from rubella vaccination programs.
• Comparison of seropositivity rates between the Phase 5 catch-up cohort and the CRS prevention cohort.
• Assessment of the effect of applying a unified serological cutoff standard.

Main Results:

• The Phase 5 cohort showed seropositivity aligned with national data.
• The CRS cohort exhibited unexpectedly low immunity, especially in young women.
• A unified cutoff reduced apparent immunity differences between cohorts.

Conclusions:

• Inconsistent serological cutoffs and participant selection create artificial immunity gaps.
• Harmonizing standards, targeting young women, and maintaining adult surveillance are crucial for rubella elimination.
• Japan's experience offers international insights into policy design's impact on immunity assessment and elimination success.