U.S. Study Indicates Coronavirus May Survive In The Air For Up to 3 Hours, 3 Days On Certain Surfaces

A study awaiting peer review from scientists at Princeton University, the University of California-Los Angeles and the National Institutes of Health (NIH) posted online Wednesday indicated that the COVID-19 virus could remain viable in the air "up to 3 hours post aerosolization," while remaining alive on plastic and other surfaces for up to three days.

"Our results indicate that aerosol and fomite transmission of HCoV-19 is plausible, as the virus can remain viable in aerosols for 42 multiple hours and on surfaces up to days," reads the study's abstract.

The test results suggest that humans could be infected by the disease simply carried through the air or on a solid surface, even if direct contact with an infected person does not occur. That finding, if accepted, would come in stark contrast to previous media reports that suggested the virus was not easily transmittable outside of direct human contact.

We found that viable virus could be detected in aerosols up to 3 hours post aerosolization, up to 4 hours on copper, up to 24 hours on cardboard and up to 2-3 days on plastic and stainless steel. HCoV-19 and SARS-CoV-1 exhibited similar half-lives in aerosols, with median estimates around 2.7 hours. Both viruses show relatively long viability on stainless steel and polypropylene compared to copper or cardboard: the median half-life estimate for HCoV-19 is around 13 hours on steel and around 16 hours on polypropylene. Our results indicate that aerosol and fomite transmission of HCoV-19 is plausible, as the virus can remain viable in aerosols for multiple hours and on surfaces up to days.

[...] HCoV-19 has been detected in upper and lower respiratory tract samples from patients, with high viral loads in upper respiratory tract samples. Therefore, virus transmission via respiratory secretions in the form of droplets (>5 microns) or aerosols (<5 microns) appears to be likely. Virus stability in air and on surfaces may directly affect virus transmission, as virus particles need to remain viable long enough after being expelled from the host to be taken up by a novel host.

[...] HCoV-19 nCoV-WA1-2020 (MN985325.1) and SARS-CoV-1 Tor2 (AY274119.3) were the strains used in our comparison. Virus stability in aerosols was determined as described previously at 65% relative humidity (RH) and 21-23°C.

A study published just last year found that ensuring even minimum levels of outdoor air ventilation reduced influenza transmission as much as having 50 percent to 60 percent of the people in a building vaccinated.

Buildings typically recirculate some air, which has been shown to lead to higher risk of infection during outbreaks, as contaminated air in one area is circulated to other parts of the building (as it did in the school with measles). When it’s very cold or very hot, the air coming out of the vent in a school classroom or office may be completely recirculated. That’s a recipe for disaster.

If air absolutely has to be recirculated, you can minimize cross-contamination by enhancing the level of filtration. Most buildings use low-grade filters that may capture less than 20 percent of viral particles. Most hospitals, though, use a filter with what’s known as a MERV rating of 13 or higher. And for good reason — they can capture more than 80 percent of airborne viral particles.

For buildings without mechanical ventilation systems, or if you want to supplement your building’s system in high-risk areas, portable air purifiers can also be effective at controlling airborne particle concentrations. Most quality portable air purifiers use HEPA filters, which capture 99.97 percent of particles.

These approaches are supported by empirical evidence. In my team’s recent work, just submitted for peer review, we found that for measles, a disease dominated by airborne transmission, a significant risk reduction can be achieved by increasing ventilation rates and enhancing filtration levels. (Measles comes with something that works even better that we don’t yet have for this coronavirus — a vaccine.)

There is also ample evidence that viruses survive better at low humidity — precisely what happens during winter, or in the summer in air-conditioned spaces. Some heating and ventilation systems are equipped to maintain humidity in the optimal range of 40 percent to 60 percent, but most are not. In that case, portable humidifiers can increase humidity in rooms, particularly in a home.