Severity of Omicron (B.1.1.529) and Delta (B.1.1.617.2) SARS-CoV-2 infection among hospitalised adults: a prospective cohort study

Abstract

Limited data exist assessing severity of disease in adults hospitalised with Omicron SARS-CoV-2 variant infections, and to what extent patient-factors, including vaccination and pre-existing disease, affect variant-dependent disease severity. This prospective cohort study of all adults (≥18 years of age) hospitalised at acute care hospitals in Bristol, UK assessed disease severity using 3 different measures: FiO2 >28%, World Health Organization (WHO) outcome score >5, and hospital length of stay (LOS) >3 days following admission for Omicron or Delta variant infection. Independent of other variables, including vaccination, Omicron variant infection was associated with a statistically lower severity compared to Delta; risk reductions were 58%, 67%, and 16% for FiO2, WHO score, and LOS, respectively. Younger age and vaccination with two or three doses were also independently associated with lower COVID-19 severity. Despite lower severity relative to Delta, Omicron infection still resulted in substantial patient and public health burden following admission.

Simulating potential outbreaks of Delta and Omicron variants based on contact-tracing data: A modelling study in Fujian Province, China

“…In contrast, the cumulative mortality of Omicron was 0.31–0.41 times the death of Delta variant. These results accord with cohort studies which found Omicron infection has a lower risk of severe outcomes than Delta ( Hyams et al, 2022 ; Nyberg et al, 2022 ). For instance, in the contact setting without stringent lockdowns, we estimated that in a potential Omicron wave, only 4.7% of infections would occur in Fujian Province among individuals aged >60 years, while 58.75% of the death toll would occur in unvaccinated individuals aged >60 years (14,271 people).…”

Evolution of SARS‐CoV‐2 variants of concern over a period of Delta and Omicron cocirculation, among patients hospitalized for COVID‐19 in an Italian reference hospital: Impact on clinical outcomes

“…Regarding the vaccination status, consistent with previous data from both general population and hospitalized patients, [19][20][21][22][23][24][25][26][27][28][29] we found a higher probability of prior full vaccination among Omicron infected individuals, likely due to the mechanism of immune evasion described for this viral variant. [12][13][14] Although this aspect has led to questions about whether the lower severity of Omicron infections may be due to an inherent characteristic of the variant or to the wide vaccination coverage, several studies have confirmed the lower severity of Omicron compared with Delta infections also in the unvaccinated population.…”

“…In particular, patients infected with Omicron VOC had a median age 7 years higher than those with Delta and more than half of them reported at least two underlying comorbidities at hospital admission as compared to less than 40% of patients infected with Delta. This data is in contrast with previous studies conducted in both outpatient 21–23 and inpatient 25–27 healthcare settings, which described a younger median age and a similar or lower comorbidity burden of patients with Omicron compared to Delta infection but are in line with recent observations from Belgian 28 and British 29 cohorts of hospitalized patients. These discrepancies among available studies can be explained by several reasons, such as different approaches and timing of the vaccination campaign, public health measures, and testing strategies.…”

“…However, whether this lower degree of severity is related to an inherent characteristic of the virus or an increase in immunity in the population over time remains to be clarified. Despite the lower severity of Omicron infections reported in general population, comparisons of the clinical profile and the risk for clinical progression between the two VOCs in subjects hospitalized for SARS‐CoV‐2 infections are still limited 25–29 . Additionally, the role of no‐viral factors as predictors for severe in‐hospital outcomes, in the period of Delta‐to‐Omicron transition, should be better defined, particularly in high vaccine coverage settings, where a high proportion of admissions are associated with, but not caused by, SARS‐CoV‐2 infection.…”

mRNA vaccines: The future of prevention of viral infections?

“…33 The number of deaths averted per administered dose was significantly higher in high-income countries, which has also been attributed to higher access and uptake of the more efficacious mRNA vaccines. 33 Moreover, studies show that scaling up mRNA vaccinations against COVID-19 in lower-to-middleincome countries during the dominance of the clinically less significant Omicron severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant [34][35][36] would bring substantial benefits in terms of averted deaths and could be an economically reasonable approach. 37 At the same time, mRNA vaccines are well-accepted by individuals who do not reveal significant vaccine hesitancy.…”