Experts predicted a possible “tripled emic” of influenza A (IAV), RSV, and COVID-19 for the winter of 2023, and concern remains about preparedness for potential SARS-CoV-2 coinfection in patients with other upper respiratory viruses. The situation is compounded by the fact that, while circulation patterns for IAV and RSV are well known, those for COVID-19 are uncertain.
To describe interactions within the respiratory tract between SARS-CoV-2 and IAV and RSV, Scottish investigators performed a study of cultures from human bronchial epithelial cells (HBECs). Their results, which included single infections and coinfections with SARSCoV-2 plus IAV or RSV, were published in The Journal of Infectious Diseases. The findings indicate that infections with other respiratory viruses may result in temporary resistance to SARS-CoV-2 and that COVID-19 cases may decline during periods of high circulation of IAV and RSV.
“IAV and RSV circulate at high levels during the winter,” Pablo Murcia, DVM, PhD, MSc, notes. “Coinfections do occur with viral infections, but we know very little about how viruses interact in nature. It is critical that we
understand how IAV and RSV might interact with SARS-CoV-2, which was the rationale for our study.”
Cell Culture Methods
The researchers “performed single infections and coinfections of complex cultures of respiratory epithelium that recapitulate to a great extent the human respiratory epithelium,” says Dr. Murcia. “We quantified the replication of the viruses and virus spread across the epithelium and examined the cellular response to infection.”
The virus strains used were RSV strain A2, SARS-CoV-2 strain BetaCoV, and IAV H3N2. HBEC cultures were infected and fixed. For SARS-CoV-2 and SARS-CoV-2/ IAV infections, anti-SARS-CoV-2 antibodies were added. For SARS-CoV-2/RSV infections, anti-SARS-CoV-2 and anti-RSV antibodies were added. To titrate IAV, MDCKSIAT cells were seeded in 12-well plates and virus samples were serially diluted. Hematoxylin and eosin staining and immunostaining and image analyses were also conducted.
By combining microscopy with quantification of viral replication with or without an innate immune inhibitor, the study authors were able to establish changes in virus-induced pathology, virus spread, and virus replication.
Changes Driven By IAV or RSV, Not SARS-CoV-2
“The main finding from our study is that SARS-CoV-2 replication and spread within the respiratory epithelium is impaired in the presence of either RSV or IAV. In addition, that reduction is time-dependent,” says Dr. Murcia.
The authors superinfected the HBE cultures at different timepoints with either IAV or RSV. The greatest decrease in SARS-CoV-2 titers occurred when IAV was added 24 hours after SARS-CoV-2 infection. SAR-CoV-2 replication was significantly inhibited when the infected cultures were challenged with RSV 24 hours after SARS-CoV-2 infection.
Dr. Murcia and colleagues note that approximately 10% of viral respiratory infections are coinfections. They speculate that if the effect they observed translates at epidemiological scale, SARS-CoV-2 infections may decline in forthcoming winters as normal mixing of circulating viruses resumes.
“It appears that interferon responses triggered by some respiratory viruses can block SARS-CoV-2 infection,” says Dr. Murcia.
