A recent review published in the BSI’s official journal Immunology explored the relationship between respiratory viral infections and asthma to better understand the potential impact of SARS-CoV-2 infection on patients with asthma.
Asthma as a risk factor for COVID-19
We do not yet have a clear picture of exactly how asthma might affect an individual’s susceptibility to catching COVID-19 or experiencing serious symptoms from the infection. Although initial evidence showed that asthma did not seem to be a strong risk factor for suffering severe symptoms of COVID-19, recent studies have found that asthma may be common in patients with COVID-19 and may be linked to longer time of intubation in those who do develop serious disease. As SARS-CoV-2 is a new coronavirus, it is valuable to look at previous scientific data from patients with asthma and other viral infections.
Asthma can influence respiratory viral infections
Patients with asthma have a higher risk of infection with respiratory viruses, such as respiratory syncytial virus or human rhinovirus (which cause the common cold), and an impaired immune response to such infections. Many different studies indicate that patients with asthma are less able to defend against respiratory viral infections and that the infection can spread more easily. In patients with asthma, certain immune cells called T helper 2 cells (Th2) are overactive and produce excessive cytokines (signalling molecules) that increase inflammation. This specific immune response is not protective against viral infection and can inhibit other pathways that do protect against viruses. Patients with asthma also have reduced levels of certain cytokines that defend against viral infections and some specialised immune cells have reduced antiviral functions. This can prevent or decrease an adequate immune response to viral respiratory infections in patients with asthma.
Respiratory viral infections can cause asthma
On the other hand, it is also known that viral respiratory infections can induce or worsen asthma. There is evidence that some children who have infections with respiratory syncytial virus or human rhinovirus can go on to develop asthma in some cases. Respiratory viral infections can initiate or aggravate asthma through altering the immune response and changing the structure of the airways. Additionally, viral infections can compromise the structure of the cells that line the airways and cause changes to the community of microbes that live there, which can promote growth of certain germs that can make asthma symptoms worse.
Unknowns of SARS-CoV-2 infection
There is little evidence of the effects of SARS-CoV-2 in the lung function of patients with asthma and more research is needed in this field. This review detailed other respiratory viral infections that can contribute to asthma and how it is now important to monitor and study the consequences of COVID-19 in patients with asthma.
Novak, N. and Cabanillas, B. (2020), Viruses and asthma: the role of common respiratory viruses in asthma and its potential meaning for SARS‐CoV‐2. Immunology. Accepted Author Manuscript. doi:10.1111/imm.13240
First published 20 July 2020
Summary author Erika Aquino, BSI Public Engagement Officer