Limited durability of protection conferred by XBB.1.5 vaccines against omicron-associated severe outcomes among community-dwelling adults, Ontario, Canada

Nelson Lee; Lena Nguyen; Sharifa Nasreen; Peter C Austin; Kevin A Brown; Sarah A Buchan; Ramandip Grewal; Kevin L Schwartz; Mina Tadrous; Kumanan Wilson; Sarah E Wilson; Jeffrey C Kwong; Canadian Immunization Research Network (CIRN) Investigators

doi:10.1016/j.vaccine.2025.127300

Limited durability of protection conferred by XBB.1.5 vaccines against omicron-associated severe outcomes among community-dwelling adults, Ontario, Canada

Vaccine. 2025 Jul 11:60:127300. doi: 10.1016/j.vaccine.2025.127300. Epub 2025 May 26.

Affiliations

¹ Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada.
² ICES, Toronto, Ontario, Canada.
³ State University of New York, Brooklyn, New York, USA.
⁴ ICES, Toronto, Ontario, Canada; Institute of Health Policy, Management and Evaluation, University of Toronto, Toronto, Ontario, Canada.
⁵ Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada; ICES, Toronto, Ontario, Canada; Public Health Ontario, Toronto, Ontario, Canada.
⁶ Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada; ICES, Toronto, Ontario, Canada; Public Health Ontario, Toronto, Ontario, Canada; Centre for Vaccine Preventable Diseases, University of Toronto, Toronto, Ontario, Canada.
⁷ Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada; ICES, Toronto, Ontario, Canada; Centre for Vaccine Preventable Diseases, University of Toronto, Toronto, Ontario, Canada.
⁸ ICES, Toronto, Ontario, Canada; Women's College Hospital, Toronto, ON, Canada; Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada.
⁹ Department of Medicine, University of Ottawa, Ottawa, Ontario, Canada; Ottawa Hospital Research Institute, Ottawa, Ontario, Canada; Bruyère Research Institute, Ottawa, Ontario, Canada.
¹⁰ Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada; ICES, Toronto, Ontario, Canada; Public Health Ontario, Toronto, Ontario, Canada; Centre for Vaccine Preventable Diseases, University of Toronto, Toronto, Ontario, Canada; Department of Family and Community Medicine, University of Toronto, Toronto, Ontario, Canada; University Health Network, Toronto, Ontario, Canada. Electronic address: jeff.kwong@utoronto.ca.

PMID: 40424706
DOI: 10.1016/j.vaccine.2025.127300

Abstract

We estimated XBB.1.5 vaccine effectiveness (VE) against hospitalization/death among adults aged ≥50 years in Ontario, Canada, from September 2023 to June 2024. Compared with non-XBB.1.5 vaccinees, the initial protection at 0-3 months was 64 % (95 %CI, 57 %-69 %) during XBB-sublineage predominance. It was reduced to 57 % (95 %CI, 48 %-64 %) when JN/KP-sublineages became predominant, and quickly declined. No significant protection was observed >6 months post-vaccination. The VE estimates were lower when the last vaccine dose in the reference group was given more recently than 12 months, or was the omicron-containing bivalent vaccine. Short durability of protection poses unique challenges for COVID-19 vaccination.

Keywords: Community-dwelling adults; Vaccine effectiveness; XBB.1.5 vaccine.

MeSH terms

Aged
Aged, 80 and over
COVID-19 Vaccines* / administration & dosage
COVID-19 Vaccines* / immunology
COVID-19* / epidemiology
COVID-19* / immunology
COVID-19* / prevention & control
Female
Hospitalization / statistics & numerical data
Humans
Independent Living
Male
Middle Aged
Ontario / epidemiology
SARS-CoV-2* / immunology
Vaccination
Vaccine Efficacy*

Substances

COVID-19 Vaccines