Limited durability of protection conferred by XBB.1.5 vaccines against Omicron-associated severe outcomes among community-dwelling adults aged ≥50 years, Ontario, Canada, September 2023 to June 2024
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We estimated XBB.1.5 vaccine effectiveness against hospitalization/death among adults aged ≥50 years. Compared with non-XBB.1.5 vaccinees, the initial protection of 64% (95%CI, 57%−69%) was reduced when JN/KP-sublineages became predominant, and quickly declined. No significant protection was observed >6 months post-vaccination. Short durability of protection poses unique challenges for COVID-19 vaccination.
