Photoinactivation of influenza viruses by modulated indoor daylight spectrum and intensity.

Influenza claims over 290,000 lives annually, and the annual flu season remains a major public health challenge. Within the domain of health-focused architectural design, indoor daylight emerges as a potential shield against microbial threats. Yet, a significant gap in our understanding remains: the effect of indoor daylight on viruses. To bridge this knowledge gap, we used a living lab setup to investigate the impact of modulated indoor daylight on the stability of genomic material and persistence of infectivity of enveloped influenza A and B viruses, along with the non-enveloped bacteriophage MS2 on an environmental surface of glass. Indoor daylight modulation showed capacity for viral inactivation with differential activity depending on spectrum, intensity, and duration of exposure. Intensity was the most impactful, significantly reducing the infectivity of influenza A virus and both the infectivity and amount of recoverable genomic material of influenza B virus following 8 h of exposure. Even at low-intensity light, comparable to light passing through traditional blinds, spectrum-modulated, blue-enriched light significantly reduced the infectivity of influenza A and B within 8 h. Moreover, for all viruses, the infectivity declined before the stability of genomic material, suggesting a mechanism of photoinactivation via the disruption of viral proteins involved in infection. This research emphasizes the paramount importance of considering daylighting conditions as a strategic approach to control infectious disease transmission in built environments. Our findings not only underscore this significance but also offer innovative pathways to transform indoor spaces into safer, healthier environments for everyone.IMPORTANCEThis study examined the interplay between indoor daylighting and viruses, specifically influenza A, influenza B, and MS2 bacteriophage in a simulated indoor environment on a surface material of glass. It demonstrated that indoor daylight modulation was able to inactivate influenza A and B following 8 h of exposure at high-intensity and low-intensity blue-enriched light; however, the stability of genomic material of influenza A was unaffected until at least 24 h of exposure. These results, which focus on differences between stability of genomic material and infectivity, provide deeper insight into viral photoinactivation mechanisms, and the use of a living-lab setup lays the foundation for a framework for healthy building design using indoor daylight modulation for infection control.