Direct link to the peer-reviewed CDC report: R. Link-Gelles, et al., Early Estimates of Bivalent mRNA Booster Dose Vaccine Effectiveness in Preventing Symptomatic SARS-CoV-2 Infection Attributable to Omicron BA.5– and XBB/XBB.1.5–Related Sublineages Among Immunocompetent Adults — Increasing Community Access to Testing Program, United States, December 2022–January 2023, MMWR Morb Mortal Wkly Rep. (25 January 2023)

Notes:

• Vaccine effectiveness was compared to fully vaccinated individuals (2-4 monovalent doses) with no bivalent booster dose.
• Protection was reduced in older groups: 40% effective in adults ages 50 to 64 and 43% effective in adults 65 and older.
• The XBB sublineage accounted for >50% of sequenced lineages in the Northeast by December 31, 2022, and 52% of sequenced lineages nationwide as of January 21, 2023.
• Tests from persons who reported a positive SARS-CoV-2 test during the preceding 90 days were excluded to avoid analyzing multiple tests from the same infection.
  • Statistical power was not adequate to stratify by presence of prior infection >90 days earlier.
• All persons should stay up to date with recommended COVID-19 vaccines, including receiving a bivalent booster dose when they are eligible.