Individuals’ microbiomes may play a role in the severity of COVID-19 infection and the strength of their immune response, according to a study published in Gut. Also, imbalances in the microbiome may cause “long-haul” COVID, the study authors added. They studied blood and stool samples from 100 patients with COVID-19 and from 78 people without the infection who were part of a microbiome study before the pandemic began. In 274 stool samples, the gut microbiome differed significantly between patients with and without COVID-19, regardless of whether they had been given drugs, including antibiotics. For example, those with COVID-19 had fewer types of bacteria that can affect the immune system response than those without the infection. The reduced number of these bacteria was linked to the severity of the infection. Moreover, the number of these bacteria remained low up to 30 days after infected patients had cleared the virus, the researchers found. Analysis of the blood samples found that the microbial imbalance in the COVID-19 patients was linked with high levels of inflammatory cytokines and blood markers of tissue damage, such as C-reactive protein. The critical question is whether these changes are unique to COVID-19 or are commonly seen in sick patients who may have been hospitalized for non-COVID-related illnesses.