No, you are not imagining! Although during respiratory tract infection (RTI) season several viruses such as rhinovirus, respiratory syncytial virus (RSV) and coronavirus may cocirculate, influenza virus frequently outcompetes many RTI viruses, likely through a phenomenon called “viral interference.” 1-4
A negative viral interference is observed when a virus that has already infected a host makes that host resistant to infection by the second virus (isn’t that fascinating?). Although there a lot of virus, host and environmental variables that affect infection risk, potential mechanisms for this interference include a rapid and robust innate immune response to the first virus such as through upregulation of interferon (IFN) production which can protect against unrelated viruses, thereby creating a temporary “antiviral state.” 1-4
A negative viral interference has been shown between influenza-A virus (IAV) and SARS-CoV-2 by a cool 2024 study using the air-liquid interface culture model of the differentiated human airway epithelium. 4 Replicating IAV induced a robust interferon response and suppressed SARS-CoV-2 replication in both sequential and simultaneous infections. In contrast, SARS-CoV-2 did not demonstrate significant viral interference with IAV. The researchers took their experiment a step further and found that oseltamivir (Tamiflu), an anti-IAV agent, restored SARS-CoV-2 replication with IAV coinfection by reducing induction of IFN!
One explanation for the inability of SARS-CoV-2 to interfere with the production of influenza virus is its slower induction of IFN stimulating genes likely due to its more effective mechanisms of antagonizing the IFN response with infected cells.4 Another explanation is that SARS-CoV-2 has a slower growth rate than IAV, making it more susceptible to being “outgunned” by faster growing viruses. Some strains of IAV may also cause more damage to the epithelial cells than SARS-CoV-2 thus reducing the number of host cells available for SARs-CoV-2 infection.2 Last, secreted IFNs (eg, IFN λ) can also bind to receptors present at the surface of infected and neighboring state blocking the second virus from infecting the host.1
So, it looks like competition among living forms in this world also applies to the world of viruses!
Bonus Pearl: Did you know that the concept of viral interference was first described in the 1960s following observation that oral administration of live enterovirus vaccines decreased detection of several unrelated respiratory viruses such as influenza virus, RSV and human adenovirus?1
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References
- Piret J, Bolvin G. Viral interference between respiratory viruses. Emerg Infect Dis 2022;28:273-280. Viral Interference between Respiratory Viruses – PubMed
- Gilbert-Girard S, Piret J, Carbonneau J, et al. Viral interference between severe acute respiratory syndrome coronavirus 2 and influenza A viruses. PLOS Pathogens 2024;20(7):e1012017. Viral interference between severe acute respiratory syndrome coronavirus 2 and influenza A viruses – PubMed
- Kaaijk P, Swaans N, Nicolaie AM, et al. Contribution of influenza viruses, other respiratory viruses and viral co-infections to influenza-like illness in older adults. Viruses 2022;14, 797. Contribution of Influenza Viruses, Other Respiratory Viruses and Viral Co-Infections to Influenza-like Illness in Older Adults – PubMed
- Cheemarla NR, Watkins TA, Mihaylova VT, et al. Viral interference during influenza A-SARS-CoV-2 coinfection of the human airway epithelium and reversal by oseltamivir. J Infect Dis 2024;229:1430-4. Viral Interference During Influenza A-SARS-CoV-2 Coinfection of the Human Airway Epithelium and Reversal by Oseltamivir – PubMed
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