The virus that causes COVID-19, SARS-CoV-2, spreads primarily through the air via respiratory particles expelled by an infected person. Another potential route of infection involves surfaces, known as fomite transmission. Fomites are inanimate objects, such as doorknobs or counters, that can carry infection. Understanding the viability of the virus on these surfaces helps clarify the actual risk and guides effective mitigation strategies.
How Long the Virus Survives on Surfaces
The viability of SARS-CoV-2 outside a host depends heavily on the material it lands on and the surrounding environment. Studies have shown that the virus can remain infectious for a range of time, from hours to a few days, with the most extended survival times observed on hard, non-porous surfaces. For materials like stainless steel and plastic, which are common in high-touch areas, the virus can remain detectable for two to three days under typical indoor conditions. Some laboratory findings suggest the virus may persist for up to seven days on plastic, though the concentration of viable virus drops significantly over time.
In contrast, the virus survives for a shorter duration on porous or softer materials. For instance, viable virus particles on cardboard are typically not detectable after 24 hours. Copper surfaces are particularly inhospitable to the virus, where infectious particles are often inactivated within about four hours.
Environmental factors also influence persistence, as high temperatures, low humidity, and exposure to sunlight tend to accelerate the rate at which the virus loses its ability to cause infection. The presence of detectable viral genetic material (RNA) does not equate to the presence of enough viable virus to cause an infection.
Understanding Fomite Transmission
Fomite transmission is a multi-step pathway that requires a sequence of events to successfully lead to infection. The process begins when an infected person expels respiratory droplets onto a surface, or when they touch a surface with contaminated hands. These droplets contaminate the object, creating the fomite.
For transmission to occur, a susceptible person must then touch the contaminated surface, which transfers viral particles to their hands. The final step is self-inoculation, which happens when the person touches their mucous membranes, such as their eyes, nose, or mouth, with the contaminated hands. If the transferred dose of viable virus is sufficient to overcome the body’s defenses, an infection may follow. Since this pathway requires multiple successful transfers, surface contamination alone is generally not sufficient to cause illness.
Best Practices for Cleaning and Disinfecting
Surface Cleaning and Disinfection
Reducing the risk of surface transmission involves two distinct but complementary actions: cleaning and disinfecting. Cleaning refers to the physical removal of dirt, debris, and germs from a surface, often using soap and water. Disinfecting uses chemical products to actively kill pathogens, including the SARS-CoV-2 virus.
The best practice is to always clean a surface before disinfecting it, as dirt can interfere with the disinfectant’s ability to kill germs effectively. Approved disinfectants include diluted household bleach solutions, alcohol solutions containing at least 70% alcohol, or EPA-registered products specifically listed as effective against SARS-CoV-2. Effective disinfection requires following the “contact time,” or dwell time, which is the amount of time the surface must remain visibly wet with the disinfectant to ensure the virus is killed. This time varies by product and must be followed exactly according to the manufacturer’s label instructions.
Hand Hygiene
The single most effective measure for breaking the chain of fomite transmission is diligent hand hygiene. Individuals should wash their hands frequently with soap and water for a minimum of 20 seconds, especially after touching surfaces in public spaces. When soap and water are not readily available, using a hand sanitizer that contains at least 60% alcohol provides a suitable alternative. Focusing these efforts on frequently touched objects, such as doorknobs, light switches, and shared electronics, provides the highest return on risk reduction.
Current Public Health View on Surface Risk
Current public health consensus holds that while fomite transmission is possible, it is considered a secondary and relatively minor route of COVID-19 spread. The primary mode of transmission is the inhalation of airborne respiratory droplets and aerosols containing the virus. This understanding has shifted the focus of mitigation efforts away from excessive surface cleaning and toward improving indoor air quality and ventilation.
Mathematical models suggest that the risk of infection from touching a contaminated surface is generally low. Some risk assessments estimate the chance of infection through a single contact with a contaminated surface to be less than one in 10,000.
This reduced emphasis on surfaces reflects the fact that the virus concentration drops quickly after deposition, and the multi-step nature of fomite transfer acts as a natural barrier to infection. Although the risk is low, public health bodies still recommend routine cleaning of high-touch surfaces as a sensible precaution against SARS-CoV-2 and other common pathogens.