According to a study published in the American Journal of Respiratory and Critical Care Medicine, individuals who are obese are more susceptible to severe COVID-19 because of a poorer inflammatory immune response, which can affect the bodys ability to fight infections.

Researchers from the Cambridge Institute of Therapeutic Immunology and Infectious Disease (CITIID) and Wellcome Sanger Institute demonstrated that after SARS-CoV-2 infection, cells lining the lungs, nasal cells, and immune cells in the blood exhibit a blunted inflammatory response in obese patients, producing insufficient levels of molecules required to fight the infection.

Several studies have shown that people who are obese already have higher levels of key molecules associated with inflammation in their blood. However, in this study, the researchers found it to be the "absolute opposite". They found that obese patients had underactive immune and inflammatory responses in their lungs. As a result, they analyzed blood and lung samples taken from 13 obese patients with severe COPD requiring mechanical ventilation and intensive care treatment and 20 controls.

The findings of the study showed that, in comparison to non-obese patients, cells in the lining of the lungs and some of the immune cells in obese patients had lower levels of activity, especially in terms of genes responsible for the production of two molecules, namely interferons (INF) and tumor necrosis factor (TNF). Professor, Mrs. Menna Clatworthy, a clinician scientist at the University of Cambridge, stated that these findings are really surprising and unexpected. Across every cell type they looked at, the team found that the genes responsible for the classical antiviral response were less active. They were completely muted. 

(Source: https://medicalxpress.com/news/2023-03-underactive-immune-response-obesity-link.html)