Nasal sprays have emerged as a topic of considerable interest in the ongoing effort to combat respiratory viral infections, particularly COVID-19. This approach aims to leverage the nasal passages, a primary entry point for many airborne viruses, as a defense against infection. Agents are introduced directly to the nasal lining to either block or neutralize viruses before they can establish an infection. This strategy holds potential as an additional layer of protection, complementing existing public health measures.
Mechanisms of Action
Nasal sprays work through several scientific principles to prevent SARS-CoV-2 infection. One mechanism involves creating a physical barrier within the nasal passages. Ingredients like iota-carrageenan, derived from red seaweed, form a gel-like layer that can trap viral particles, potentially preventing them from binding to and entering host cells. This physical obstruction acts as a first line of defense, reducing the initial viral load that reaches the respiratory tract.
Another approach focuses on direct antiviral action, where the spray contains substances designed to inactivate the virus. For instance, nitric oxide (NO) has demonstrated antimicrobial properties against SARS-CoV-2, working to eliminate airborne viruses in the nasal cavity. Some formulations also aim to disrupt the virus’s ability to replicate or to interfere with its entry into cells by targeting specific host proteases or receptors like ACE2.
Beyond physical barriers and direct viral inactivation, some nasal sprays are designed to modulate the local immune response in the nasal mucosa. By stimulating innate immunity, these sprays can recruit immune cells and prime the epithelial cells lining the nasal passages to respond more quickly to infections. This enhanced local immune vigilance allows the body to rapidly eliminate viruses before they spread throughout the body.
Types of Nasal Sprays and Their Development Status
Various types of nasal sprays are under development or are available in certain markets for COVID-19 prevention. Barrier-forming sprays, such as those containing iota-carrageenan, create a protective film over nasal cells. This ingredient, also found in some common products, aims to physically block the virus from attaching to cells. In some regions, iota-carrageenan-based sprays have been approved for common cold prevention for over a decade, and some studies suggest their potential in reducing COVID-19 risk.
Antiviral sprays directly target the virus to inactivate it or inhibit its replication. Nitric oxide nasal sprays (NONS), like Enovid, are examples of this type, generating a low dose of nitric oxide to eliminate viruses in the nasal cavity. Enovid has shown promising results in reducing viral load and has received emergency use authorization in some countries. Other antiviral agents, such as povidone-iodine, have also been investigated for their virucidal activity against SARS-CoV-2.
Immune-modulating sprays aim to enhance the body’s natural defenses at the site of infection. One such investigational spray, INNA-051, is designed to stimulate innate immunity in the nose, preparing the nasal mucosa to respond more rapidly to viral threats. Additionally, nasal spray vaccines are being developed to induce a localized immune response, including the production of antibodies, directly in the nasal passages. While some nasal spray vaccines have been authorized in countries like India and China, none are currently authorized in the U.S.
Current Evidence and Considerations
Scientific studies have explored the efficacy and safety of nasal sprays for COVID-19 prevention. For instance, a randomized, placebo-controlled trial involving a nasal spray with natural virucidal agents found a significant reduction in SARS-CoV-2 infection among high-risk healthcare workers, with a 62% fewer infections in the test group compared to placebo. This study also reported fewer clinical symptoms in the group using the spray, and no serious adverse events were noted.
Another study focusing on iota-carrageenan in healthcare workers in Argentina observed a lower rate of COVID-19 diagnosis in those using the spray, with 1% infection rate compared to 5% in the placebo group. Some research indicates that nitric oxide nasal sprays can effectively reduce viral load in individuals with mild COVID-19 cases, suggesting a potential role in reducing transmission.
Considerations for potential users include possible side effects, such as temporary tingling or stinging at the application site for some iodine-containing sprays. The long-term effects of regular use of some of these sprays are still being studied, and their effectiveness may vary based on individual factors and circulating viral variants.
Official Guidance and Future Outlook
Major health organizations, such as the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC), currently emphasize established preventive measures for COVID-19. These recommendations include vaccination, physical distancing, mask-wearing, and frequent hand hygiene. While some health professionals have petitioned the CDC for guidance on incorporating nasal sprays into a layered defense strategy, official recommendations from these bodies typically focus on interventions with extensive, broadly accepted evidence.
The regulatory landscape for nasal sprays designed for COVID-19 prevention varies globally. In the U.S., there are no nasal sprays specifically authorized to prevent COVID-19, although some nasal spray vaccines have received authorization in other countries, such as India and China. The development of new formulations, including those with drug-free ingredients that create physical barriers and neutralize pathogens, continues to progress through preclinical and clinical trials.
The future role of nasal sprays in public health strategies against COVID-19 and other respiratory illnesses is still evolving. As research continues to provide more robust data on efficacy and safety, these sprays could potentially offer an additional layer of protection, particularly for individuals who may be vaccine-hesitant, immunosuppressed, or in situations where other preventive measures are challenging to implement consistently.