People with obesity have an increased risk of severe COVID-19: a meta-analysis by Popkin and colleagues found that the odds ratio of people with obesity being hospitalised with COVID-19 was 2·13 when compared with those without obesity, and mortality was 48% higher in patients with obesity than in those without. This increased risk of severe disease is linked to higher rates of metabolic and cardiovascular complications.

Another major contributing factor is the presence of substantial immune dysregulation and chronic systemic inflammation. Obesity is associated with increased levels of numerous inflammatory mediators, including interleukin (IL)-1, IL-6, IL-17, and tumour necrosis factor α.These cytokines are also implicated in the pathogenesis of COVID-19.

In addition to inflammation, obesity is associated with important defects in immune cells tasked with host protection, including natural killer cells and mucosal associated invariant T (MAIT) cells.
Several publications have highlighted MAIT cells as potentially having a crucial role in the host response to SARS-CoV-2.

In each of these studies, reduced peripheral serum MAIT-cell frequencies were observed in a COVID-19 severity-dependent manner (ie, with lower frequency associated with more severe COVID-19). Conversely, increased numbers of MAIT cells were noted in the lungs of patients with COVID-19 together with higher expression of MAIT-cell chemoattractants and increased levels of activated MAIT cells producing granzyme B were noted in patients with COVID-19. Furthermore, importantly, after co-culturing MAIT cells with SARS-CoV-2-infected macrophages, increased activity of the MAIT cells producing granzyme B was observed, suggesting a possible ability of MAIT cells to respond to or directly kill infected cells…Readmore