JMIR Publications

ABSTRACT

Background:

In late 2020, SARS-CoV-2 variants of concern (VOC) emerged and rapidly replaced the original strain globally. The increased transmissibility of these new variants led to increases in infections, hospitalisations and mortality, however investigation into the relative severity of VOCs remained difficult due to key confounding variables.

Objective:

We aimed to provide robust estimates of relative severity of all prevalent VOCs from during our study period in the context of vaccination rollout and heterogeneous social determinants of health (SDOH).

Methods:

We used a population-based retrospective cohort design with data from the British Columbia COVID-19 Cohort, a linked provincial surveillance platform. To assess the relative severity [hospitalisation, intensive care unit (ICU), death] of Gamma, Delta and Omicron infections during 2021 relative to Alpha, we used inverse probability treatment weighted Cox proportional hazards modelling. We also conducted a sub-analysis among unvaccinated individuals as assessed severity differed across VOC and SDOH.

Results:

We included 91,964 individuals infected with a SARS-CoV-2 VOC (20,487 Alpha, 15,223 Gamma, 49,161 Delta, 7,093 Omicron). Delta was associated with the most severe disease in terms of hospitalisation, ICU admissions and deaths (hospitalisation adjusted hazard ratio (aHR)=2.00; 95%CI: 1.92–2.08, ICU aHR=2.05; 95%CI: 1.91–2.20, death aHR=3.70; 95%CI: 3.23–4.25, relative to Alpha), followed by generally by Gamma and then Omicron and Alpha. The relative severity by VOC remained similar in the unvaccinated sub-analysis, although the proportion of Delta and Omicron infected individuals who were hospitalised was two times higher in unvaccinated individuals compared to those fully vaccinated. While exploring SDOHs, the proportion hospitalised was higher in areas with lower income across all VOCs, while in Alpha and Gamma infections, two VOCs which co-circulated, differential distributions of hospitalisations were found for among racially minoritised groups.

Conclusions:

Our study provides robust severity estimates for the most prevalent VOCs during the COVID-19 pandemic in British Columbia, Canada. Relative to Alpha, we found Delta to be most severe, followed by Gamma and Omicron. This study sheds light on vaccination and SDOH as important factors while investigating VOC severity, with the latter being an area for future investigation.