Asthma does not appear to increase the risk for a person contracting Covid-19 or affect its severity, according to new research. The team from Rutgers University in the US found that people with asthma - even those with diminished lung function who are being treated to manage asthmatic inflammation - seem to be no worse affected by SARS-CoV-2 than a non-asthmatic person.

"Older age and conditions such as heart disease, high blood pressure, chronic obstructive pulmonary disease, diabetes and obesity are reported risk factors for the development and progression of COVID-19," said Reynold A. Panettieri Jr, a pulmonary critical care physician and director of the Rutgers Institute for Translational Medicine and Science.

However, asthma is not yet proven as one such risk factor. "There is limited data as to why this is the case -- if it is physiological or a result of the treatment to manage the inflammation," said Panettieri Jr in a paper published in the Journal of Allergy and Clinical Immunology.

Inhaled corticosteroids, which are commonly used to protect against asthma attacks, also may reduce the virus' ability to establish an infection. However, studies have shown that steroids may decrease the body's immune response and worsen the inflammatory response. Children and young adults with asthma suffer mainly from allergic inflammation, while older adults who experience the same type of airway inflammation can also suffer from eosinophilic asthma -- a more severe form.

In these cases, people experience abnormally high levels of a type of white blood cell that helps the body fight infection, which can cause inflammation in the airways, sinuses, nasal passages and lower respiratory tract, potentially making them more at risk for a serious case of COVID-19. In addition, an enzyme attached to the cell membranes in the lungs, arteries, heart, kidney and intestines that has been shown to be an entry point for SARS-CoV-2 into cells is increased in response to the virus. "This enzyme is also thought to be beneficial in clearing other respiratory viruses, especially in children. How this enzyme affects the ability of SARS-CoV-2 to infect people with asthma is still unclear," said the study.

However, older people with asthma who also have high blood pressure, diabetes or heart disease may have similar instances of Covid-19 as non-asthmatics with those conditions, the researchers stressed. Future studies should address whether inhaled steroids in patients with asthma or allergies increase or decrease the risks of SARS-CoV-2 infection, and whether these effects are different depending on the steroid type.