Dr. Stephanie Taylor

July 18th, 2025

Is Poor Indoor Air Quality Fueling the Next Pandemic?

Three years after the global community recovered from the COVID-19 pandemic, health experts are now turning their attention to another potential threat: the H5N1 avian influenza virus.

Reports of infections jumping from birds to mammals, and now to humans, have raised alarms among virologists and public health officials.

While much attention has focused on vaccines and containment protocols, one critical aspect often remains overlooked: the role of the indoor environment in both disease transmission and human immune response.

As concerns mount, it’s crucial to examine how the same indoor air quality challenges that shaped the COVID-19 pandemic could once again influence the trajectory of this emerging virus.

Lessons Learned from COVID-19

• The COVID-19 pandemic provided clear evidence on how these viruses spread: Airborne transmission is the primary route for viruses like SARS-CoV-2.
• Most infections occur indoors, where people share air for extended periods.
• While vaccines, testing, and masking play an important role, they alone are not enough. Ultimately, the most essential, and often overlooked factor in both limiting virus transmission and supporting immune health is the quality of the air we breathe indoors.

The Rising Risk of H5N1

The H5N1 avian influenza virus has already proven it can jump from birds to humans, and more recently, to a growing number of mammals. While “sustained human-to-human transmission” hasn’t been officially confirmed, warning signs are mounting. The recent case of a young girl who died from H5N1, followed by her father testing positive, suggests that limited human transmission may already be occurring.

If the virus adapts to spread efficiently between people, particularly through the air in shared indoor spaces, it could spark a global outbreak. Like SARS-CoV-2, H5N1 could take advantage of poorly ventilated environments, where individuals unknowingly share virus-laden aerosols over time. Enclosed settings such as workplaces, schools, and healthcare facilities could quickly become hotspots for transmission, accelerating the spread.

Preventing this scenario requires more than vaccines and surveillance. We must also address the environmental conditions that either slow, or supercharge, viral spread.

This is where indoor air quality (IAQ) plays a powerful dual role, both in influencing how viruses move through the air, and in shaping how well our immune systems can defend against them.

IAQ’s Dual Impact on Viruses and Immunity

Once an airborne disease begins spreading, the immediate response often focuses on removing viruses from the air, through filtration, ventilation, air cleaning, and humidification. These are all essential strategies to reduce exposure to shared spaces. But what’s often overlooked is just as important: creating indoor environments that actively support the body’s ability to defend itself.

Pollutants like particulate matter have been shown to suppress immune function within days. In fact, research shows that even a 1 μg/m³ increase in PM can significantly impair the body’s early immune response to viral infections. In other words, indoor air doesn’t just carry disease—it can also strengthen or weaken our immune system’s ability to fight it.

Humidity also plays a critical role in immune defense. Relative humidity (RH) below 40%, common in heated indoor spaces during colder months, creates an ideal environment for viruses to remain airborne longer. It also dries out the mucosal barrier in our airways, which is our body’s first line of defense, and slows down tissue repair after infection.

To truly reduce the risk of outbreaks and enhance our ability to respond to them, we need to go beyond simply removing pathogens from the air. We must design and maintain indoor spaces that help people stay healthy in the first place.

Setting Up Building Health as a Preventive Strategy

To truly prepare indoor spaces for current and future health threats, building and facility operators must take a more proactive approach beyond routine tracking of basic indoor air quality metrics. Facility managers must:

• Continuously monitor the critical IAQ parameters: PM, volatile organic compounds (VOCs), CO₂, and relative humidity (RH)
• Maintain RH levels between 40% and 60% year-round to support immune health and limit viral spread
• Evaluate both indoor and outdoor air quality before adjusting ventilation rates to avoid introducing more pollutants
• Use IAQ software to continuously monitor all factors that influence health, with real-time medical insights into current air quality and remediation recommendations based on your specific indoor environment, like the Health Index.

By adopting a data-driven IAQ strategy rooted in occupant health, we can transform buildings into protective environments rather than passive risks.

Now is the time to take control of your indoor air. Start using the Health Index to measure, manage, and improve the conditions for human health.