Impact of infection timing before vaccination on the effectiveness of COVID-19 mRNA vaccine in healthcare workers

Understanding how prior infection timing affects the effectiveness of booster vaccination is essential for optimizing COVID-19 immunization strategies. While mRNA vaccines have demonstrated strong protection, their impact may vary depending on the interval between natural infection and vaccination. This study evaluates vaccine effectiveness among healthcare workers stratified by infection history, revealing that individuals whose last infection occurred more than one year before vaccination experienced the greatest benefit. In contrast, those with recent infections showed a less pronounced response. These findings suggest that immune memory and timing of antigen exposure play a critical role in booster performance. By identifying subgroups with differential vaccine responsiveness, this research provides actionable insights for tailoring booster recommendations, particularly during periods of high transmission risk.