Study: Waning of COVID-19 vaccine-induced immunity

Editor's Note

This Italian review and meta-analysis finds that the effectiveness of COVID-19 vaccines against Omicron and Delta variants rapidly wans over time.

Of 799 original articles, 149 reviews, and 35 preprints identified, 40 studies were included in the analysis.

Among the findings:

• Vaccine effectiveness of a primary vaccination cycle against Omicron infection and symptomatic disease were both lower than 20% at 6 months after the last dose administered.
• Booster doses restored vaccine effectiveness to levels comparable to those acquired right after the primary vaccination cycle, but 9 months after booster administration, vaccine effectiveness against Omicron was lower than 30%.
• The half-life of vaccine effectiveness against symptomatic infection was 87 days for Omicron and 316 days for Delta variants.

The findings of this study can help foster discussions on appropriate targets and timing for future vaccination programs, the researchers say.