Long-term Real-world Protection Afforded by Third mRNA Doses Against Symptomatic Severe Acute Respiratory Syndrome Coronavirus 2 Infections, Coronavirus Disease 19-related Emergency Attendances and Hospitalizations Amongst Older Singaporeans During an Omicron XBB Wave

Liang En Wee; Deanette Pang; Calvin Chiew; Janice Tan; Vernon Lee; Benjamin Ong; David Chien Lye; Kelvin Bryan Tan

doi:10.1093/cid/ciad345

Long-term Real-world Protection Afforded by Third mRNA Doses Against Symptomatic Severe Acute Respiratory Syndrome Coronavirus 2 Infections, Coronavirus Disease 19-related Emergency Attendances and Hospitalizations Amongst Older Singaporeans During an Omicron XBB Wave

Clin Infect Dis. 2023 Oct 13;77(8):1111-1119. doi: 10.1093/cid/ciad345.

Authors

Liang En Wee^{1

2

3}, Deanette Pang⁴, Calvin Chiew^{1

4}, Janice Tan⁴, Vernon Lee^{4

5}, Benjamin Ong^{4

6}, David Chien Lye^{1

6

7

8}, Kelvin Bryan Tan^{4

5}

Affiliations

¹ National Centre for Infectious Diseases, Singapore, Singapore.
² Duke-NUS Graduate Medical School, National University of Singapore, Singapore, Singapore.
³ Department of Infectious Diseases, Singapore General Hospital, Singapore, Singapore.
⁴ Ministry of Health, Singapore, Singapore.
⁵ Saw Swee Hock School of Public Health, National University of Singapore, Singapore, Singapore.
⁶ Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore.
⁷ Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore, Singapore.
⁸ Department of Infectious Diseases, Tan Tock Seng Hospital, Singapore, Singapore.

PMID: 37280047
DOI: 10.1093/cid/ciad345

Abstract

Background: Literature on long-term real-world vaccine effectiveness of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) booster vaccines (up to and beyond 360 days) is scarce. We report estimates of protection against symptomatic infection, emergency department (ED) attendances and hospitalizations up to and beyond 360 days post-receipt of booster messenger RNA (mRNA) vaccines among Singaporeans aged ≥60 years during an Omicron XBB wave.

Methods: We conducted a population-based cohort study including all Singaporeans aged ≥60 years with no documented prior SARS-CoV-2 infection who had previously received ≥3 doses of mRNA vaccines (BNT162b2/mRNA-1273), over a 4-month period during transmission of Omicron XBB. We reported the adjusted incidence-rate-ratio (IRR) for symptomatic infections, ED attendances and hospitalizations at different time-intervals from both first and second boosters, using Poisson regression; with the reference group being those who received their first booster 90 to 179 days prior.

Results: In total, 506 856 boosted adults were included, contributing 55 846 165 person-days of observation. Protection against symptomatic infections among those who received a third vaccine dose (first booster) waned after 180 days with increasing adjusted IRRs; however, protection against ED attendances and hospitalizations held up, with comparable adjusted IRRs with increasing time from third vaccine doses (≥360 days from third dose: adjusted IRR [ED attendances] = 0.73, 95% confidence interval [CI] = .62-.85; adjusted IRR [hospitalization] = 0.58, 95% CI = .49-.70).

Conclusions: Our results highlight the benefit of a booster dose in reducing ED attendances and hospitalizations amongst older adults aged ≥60 years with no documented prior SARS-CoV-2 infection, during an Omicron XBB wave; up to and beyond 360 days post-booster. A second booster provided further reduction.

Keywords: COVID-19; SARS-CoV-2; booster; mRNA; vaccine.