Despite how common upper respiratory tract infections such as the common cold and influenza are, few treatments directly target the viruses themselves, rather than just relieving symptoms. This is partly because the common cold can be caused by many different viruses, including rhinoviruses, adenoviruses, seasonal coronaviruses, and others, and there are no licensed antivirals to treat any of these.
Antivirals exist for influenza and SARS-CoV-2, but their use is limited for several reasons. Most uncomplicated infections in immunocompetent people resolve on their own within about a week, so treatment is often unnecessary. Antivirals tend to work best if started very early—ideally within 48 hours of symptom onset—when symptoms may still be mild and the benefit of treatment is less certain. Once severe disease has developed, these drugs are generally less effective, although some benefit may still remain in severe or hospitalised cases.
In addition, because antivirals are effective only against a narrow range of viruses, a rapid diagnostic test is needed to identify the cause and determine which drug to use within that short window, which further complicates treatment.
Taken together, the short treatment window, narrow spectrum of available drugs, and self-limiting nature of many respiratory infections may also reduce incentives for developing new countermeasures. Broad-spectrum antivirals or prophylactics could be more attractive, but they have proven difficult to develop.
Assistant Professor Mart Lamers, Duke-NUS' Signature Research Programme in Emerging Infectious Diseases