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uHoo Proprietary Health Index · Research-backed

Some rooms are better at spreading viruses, yours has a score.

Temperature, humidity, CO2, and ventilation all shape how long an airborne virus survives and how far it travels. The uHoo Virus Index turns those invisible conditions into a single, clear risk score updated daily from your live sensor data.

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✓ Built on published science ✓ Real-time detection and alerts ✓ Covers 9 parameters including PM2.5, NO₂, and ozone
Virus Index · Live reading
3
Low risk · Conditions unfavourable
Humidity52%
Temperature23°C
CO2910 ppm
VentilationModerate
Virus survival low in current conditions
10
Point scoring scale
Daily
Index recalculation
4
Key parameters driving the score
2
Peer-reviewed white papers
What the Virus Index measures

Whether a virus survives in your air depends on the air. Not luck.

Temperature, humidity, and how much fresh air is circulating all determine how long an airborne virus stays viable and how far it travels. The same virus released in two different rooms can have very different outcomes depending on what the air is doing.

The uHoo Virus Index scores those conditions from 1 to 10, updated daily from your live sensor readings. A score of 2 in a well-ventilated room with humidity in the right range means the environment is working against the virus. A score of 8 in a packed meeting room with CO2 at 1,500 ppm means the opposite.

The index does not tell you whether a virus is present. It tells you whether your air would help it survive if one were.

Indoor air conditions measured by the uHoo Virus Index
Scoring system

Your score tells you what your air is doing to viral risk right now.

Low scores mean conditions are working against virus survival. High scores mean your air is doing the opposite. Every level comes with specific, practical things you can actually do.

1-3
Low
Good conditions. Virus survival is low and spread is unlikely.
Your air is in good shape. Humidity, temperature, and ventilation are all working against virus survival. Keep it this way and uHoo will tell you if anything changes.
Maintain current ventilationKeep humidity between 40% and 60%No immediate action required
4-6
Moderate
Some conditions are shifting. Worth improving before the score climbs.
Most people will not notice. But anyone elderly, immunocompromised, or managing a respiratory condition could be affected. Better ventilation now is the simplest thing you can do.
Increase fresh air ventilationReduce occupancy if possibleOpen windows if outdoor air permits
7-8
High
Virus can survive for extended periods and spread is more likely. Act now.
This is the level where shared spaces become genuinely risky. Get fresh air in, reduce how many people are in the space, and if someone is unwell, they should not be in here.
Ventilate immediatelyReduce indoor occupancyUse an air purifier with HEPA filtrationConsider wearing a mask in shared spaces
9-10
Critical
Virus survival is high and spread is likely. Do not wait.
The air in this space is actively supporting transmission. If anyone in the room has symptoms, they need to leave. Get the space ventilated now and keep it empty until conditions improve.
Evacuate or limit space to one personMaximum ventilation immediatelyRun HEPA air purificationProfessional assessment recommended
What drives your score

Three things your indoor air is doing to any virus in the room.

The Virus Index is calculated from your live uHoo sensor data. These are the three conditions that matter most and the points where the risk starts to climb.

Relative humidity icon
Relative Humidity
Airborne viruses survive longest in very low or very high humidity. The optimal window for reducing virus persistence is between 40% and 60% relative humidity. Most indoor spaces in winter fall well below this, creating conditions that favour viral spread for hours.
Optimal zone: 40% to 60% RH
Temperature icon
Temperature
Cooler temperatures slow the evaporation of respiratory droplets, keeping virus-containing aerosols airborne longer. Cold, dry indoor air in winter is the environment where airborne transmission has historically been most efficient.
Higher risk in cool, dry conditions below 18°C
CO2 and ventilation icon
CO2 and Ventilation
CO2 is the best proxy for how much exhaled air is accumulating in a space. High CO2 means the air is being recirculated rather than replaced. In a high-CO2 room, virus-laden aerosols from an infectious person build up faster and linger longer. This is the most important and controllable driver of the index.
Risk climbs sharply above 1,000 ppm CO2
Family at home with healthier indoor air
For families at home

Most respiratory illness is caught at home, not in public.

When one family member brings a virus in, the air quality inside the home determines how quickly it reaches everyone else. A well-ventilated home with humidity in the right range can significantly reduce household transmission. The Virus Index tells you exactly when your home conditions make spread more or less likely, every single day.

✓Tracks the four parameters that govern airborne virus survival
✓Alerts you when indoor conditions shift toward higher transmission risk
✓Available on Guard and Command home plans
For offices and businesses

Shared spaces carry shared risk. The air tells you exactly how much.

Conference rooms, open-plan floors, and high-occupancy common areas are where workplace transmission is concentrated. Facilities teams using uHoo Aura can monitor the Virus Index across every space in real time, respond before conditions worsen, and demonstrate to occupants that air quality is being actively managed.

✓Room-by-room Virus Index across unlimited locations
✓API and BMS integration for automated ventilation response
✓Supports WELL and LEED Indoor Environmental Quality requirements
Explore uHoo Aura for businesses ->
Office and business indoor air quality monitoring
The research behind the index

Two published papers. Five years of methodology.

The Virus Index scoring model has been through two rounds of peer-reviewed publication. The first in 2020, the second in 2021 after COVID-19 gave researchers a much deeper picture of how indoor air affects airborne transmission. Sign up to receive and download both papers.

White paper v2.0 · October 2021
Addressing the Airborne Transmission Threat: Understanding the Components of Air Quality
uHoo Research · Updated methodology · PDF
The updated paper expands the original index to incorporate airborne transmission dynamics from COVID-19 research, refining the parameter weightings and scoring model with new real-world data.
White paper v1.0 · May 2020
Using Indoor Air Quality Data to Create the uHoo Virus Index
uHoo Research · Original publication · PDF
The original paper establishing the relationship between indoor air parameters and virus survival probability, forming the foundation of the Virus Index scoring model.
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Check your email. While you wait, you can also download both versions directly below.
↓ Download PDF v1.0 directly ↓ Download PDF v2.0 directly
Common questions

What people ask about the Virus Index.

The Virus Index is available with Guard (the home health intelligence add-on) and uHoo Aura (for business). For home users, Guard includes all four proprietary health indices: Mold, Virus, Influenza, and Pollen, plus Discomfort and AQI. You can add Guard at any time from your dashboard at $79/year. Guard is also free for your first 3 months when you buy Caeli.
The Virus Index is recalculated daily using your live sensor readings and the scoring model detailed in the published white papers. Your score reflects conditions in your specific space. As temperature, humidity, CO2, and ventilation change throughout the day, your score adjusts to reflect current conditions.
CO2 is the most reliable real-time indicator of how much exhaled air is accumulating in a space. When CO2 climbs, it means the air is being recirculated rather than replaced with fresh outdoor air. In a space where someone is infected, high CO2 means the virus-carrying aerosols they exhale are building up and lingering rather than being diluted. Reducing CO2 through ventilation is the single most effective action you can take to reduce airborne transmission risk.
No. The Virus Index does not detect the presence of a specific virus. It measures the indoor air conditions that govern how long airborne viruses of all types tend to survive and spread. A low score means your current conditions are unfavourable for viral transmission. A high score means conditions favour it. Whether a virus is actually present depends on the people in the space, not on the air quality alone.
Yes. The Virus Index measures the indoor air conditions that govern airborne transmission for respiratory viruses generally, including influenza, respiratory syncytial virus (RSV), rhinovirus (the common cold), and others. The parameters that control how long COVID-19 survives in the air are the same ones that govern other respiratory viruses. The index is not specific to any one pathogen.
Two white papers covering the Virus Index methodology have been published by uHoo Research. The original paper, published in May 2020, established the connection between indoor air parameters and virus survival probability. A second paper, published in October 2021, expanded the methodology with additional COVID-19 airborne transmission research. Both are available for download free of charge from the research section above.
The full index suite

Virus is one of four things the index watches for you.

Guard, Command, and uHoo Aura include three other proprietary health indices, each tracking a different invisible indoor air risk.

Mold Index logo
Mold Index
Tracks humidity, temperature, and air circulation to score the conditions that allow mold to grow. Catches risk early, when the fix is opening a window rather than calling a remediation company.
Learn about the Mold Index ->
Influenza Index logo
Influenza Index
Specific to seasonal flu transmission risk. Cold months create indoor air conditions that accelerate influenza spread between household members. Know when risk is highest so you can act at the right moment.
Learn about the Influenza Index ->
Pollen Index logo
Pollen Index
Outdoor forecasts only tell half the story. The Pollen Index tracks how pollen infiltrates your indoor air and when your home conditions intensify its impact on allergy and asthma sufferers.
Learn about the Pollen Index ->
uHoo Guard Command and Aura air quality monitoring
Available on Guard and uHoo Aura

Know what your air is doing to viral risk. Right now.

All four health indices updated daily from your live sensor data. Virus, Mold, Influenza, and Pollen. For home or for business.

Get Guard uHoo Aura for business ->
Available with Guard ($79/yr) • Free for first 3 months with Caeli • uHoo Aura for business