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. 2023 Oct;29(10):1328-1333.
doi: 10.1016/j.cmi.2023.06.016. Epub 2023 Jun 17.

Real-world effectiveness of nirmatrelvir/ritonavir against COVID-19 hospitalizations and severe COVID-19 in community-dwelling elderly Singaporeans during Omicron BA.2, BA.4/5, and XBB transmission

Liang En Wee  1 , An Ting Tay  2 , Calvin Chiew  3 , Barnaby Edward Young  4 , Betty Wong  2 , Ruth Lim  2 , Ching Li Lee  2 , Joyce Tan  2 , Shawn Vasoo  5 , David Chien Lye  5 , Kelvin Bryan Tan  6
Affiliations

Real-world effectiveness of nirmatrelvir/ritonavir against COVID-19 hospitalizations and severe COVID-19 in community-dwelling elderly Singaporeans during Omicron BA.2, BA.4/5, and XBB transmission

Liang En Wee et al. Clin Microbiol Infect. 2023 Oct.

Abstract

Objectives: Real-world data on continued effectiveness of nirmatrelvir/ritonavir against hospitalization and severe COVID-19 in the context of widespread booster mRNA vaccine uptake and more immune-evasive Omicron sub-variants are lacking. We conducted a retrospective cohort study in adult Singaporeans aged ≥60 years presenting to primary care with SARS-CoV-2 infection, during waves of Omicron BA.2/4/5/XBB transmission.

Methods: Binary logistic regression was used to estimate the effect of treatment (receiving nirmatrelvir/ritonavir) on outcomes (hospitalization, severe COVID-19). Additional sensitivity analyses, including inverse-probability-of-treatment-weighting-adjusted analysis and adjustment using overlap weights, were performed to account for observed differences in baseline characteristics among treated/untreated cohorts.

Results: We included 3959 nirmatrelvir/ritonavir recipients and 139 379 untreated controls. Almost 95% received ≥3 doses of mRNA vaccines; 5.4% had preceding infection. Overall 26.5% of infections occurred during the Omicron XBB period and 1.7% were hospitalized. On multivariable logistic regression, receipt of nirmatrelvir/ritonavir was independently associated with lower odds of hospitalization (adjusted odds ratio [aOR] = 0.65, 95% CI = 0.50-0.85). Consistent estimates were obtained after inverse-probability-of-treatment-weighting adjustment (aOR for hospitalization = 0.60, 95% CI = 0.48-0.75) and adjustment using overlap weights (aOR for hospitalization = 0.64, 95% CI = 0.51-0.79). Although receipt of nirmatrelvir/ritonavir was associated with lower odds of severe COVID-19, it was not statistically significant.

Discussion: Outpatient usage of nirmatrelvir/ritonavir was independently associated with reduced odds of hospitalization amongst boosted older community-dwelling Singaporeans during successive waves of Omicron transmission, including Omicron XBB; however, it did not significantly reduce the already low risk of severe COVID-19 in a highly vaccinated population.

Keywords: COVID-19; Hospitalization; Nirmatrelvir-ritonavir; Omicron; SARS-CoV-2.

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Conflict of interest statement

The authors report no conflicts of interest.

Figures

Figure 1
Figure 1
Flowchart showing final study population (N=143,338)
See this image and copyright information in PMC

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