SARS-CoV-2 can escape the antiviral defenses and humoral immune systems of the host owing to its rapid evolution[20], which causes reinfection in people previously infected with different variants and even leads to recurrent outbreaks[21]. This retrospective study demonstrated that disease severity in omicron patients was associated with age, neutrophil percentage, lymphocyte percentage, CRP level, and complications. ROC analysis showed that CRP accurately predicted disease severity in omicron patients better than the other parameters.
It is still unclear how COVID-19 manifests its pathological characteristics. A previous study showed that age is an independent predictor of severe/critical cases, suggesting that older people are more likely to suffer from severe or acute illness[22-24]. The median age of the severe/critical cases in this study was 77 (68–84) years, which was significantly higher than 65 (51–77) years for the ordinary cases. Furthermore, elderly individuals are more likely to experience complications, another risk for patients with COVID-19[25].
In this study, we found that patients with severe/critical illness had higher neutrophil counts than those with ordinary illness, and that neutrophil count was a predictor of disease severity. These findings suggest that factors contributing to higher neutrophil counts, such as secondary infections, may promote disease progression[26-28]. Lymphocytes are mainly produced by lymphoid organs and provide protective immunity against infection[29]. Patients with COVID-19 often have a reduced peripheral lymphocyte count, indicating that lymphocytes may be a critical risk factor for disease severity and mortality[29-31]. According to related studies, patients with COVID-19 with lymphopenia at admission might suffer from significant organ damage, require intensive therapy, and have a poor prognosis[30-32]. SARS-CoV-2 infection leads to lymphopenia by redistributing T cells and terminating their activation[33]. It has recently been discovered that the NLR is an early predictor of severe illness in COVID-19[26, 31, 34]. This retrospective study found a higher NLR in severe/critical cases than in ordinary cases. A multivariate logistic regression, however, showed that the NLR did not independently predict severe/critical cases.
CRP levels can rapidly increase following inflammation, cell damage, or tissue damage, making it one of the most specific acute-phase reactants[35]. Furthermore, several studies have demonstrated that elevated CRP levels were associated with disease severity and prognosis[11, 36]. This study showed higher CRP levels in severe/critical cases, with a median of 66.75 (34.81–99.94), suggesting excessive inflammation. Our results showed that CRP ≥28.17 mg/L could predict the severity of disease in omicron patients with a sensitivity of 89.7% and a specificity of 78.6%. Similar to our study, a single-center retrospective cohort study showed the potential predictive value of CRP levels at admission[37]. However, we found that our CRP cutoff values were generally lower than those in other studies[14, 38], possibly because of the different subtypes of SARS-CoV-2. In this study, patients with COVID-19 were infected with omicron, a less virulent variant. Despite being a nonspecific inflammatory biomarker, CRP could serve as a promising predictor of disease severity in omicron patients, owing to its low cost and availability in hospitals. It is unclear, however, exactly what role CRP plays in COVID-19 patients. The pathogenesis of COVID-19 should be the focus of following studies.