Coronavirus disease 2019 (COVID-19) is an infectious illness caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus. First identified in December 2019, this respiratory disease rapidly spread globally, leading to a widespread pandemic. Understanding how the virus spreads is important for comprehending how infections occur.
How the Virus Travels
SARS-CoV-2 primarily spreads through respiratory droplets and aerosols released by an infected individual. These particles are expelled when a person breathes, talks, coughs, or sneezes. Larger respiratory droplets tend to fall quickly to the ground within a few seconds.
Smaller particles, known as aerosols, can remain suspended in the air for longer periods and travel over greater distances, especially in indoor environments. This airborne transmission allows the virus to spread beyond close proximity. An infected person can spread the virus even before symptoms appear or if they never develop noticeable symptoms.
While less common, indirect transmission can also occur through contaminated surfaces, known as fomites. A person might get COVID-19 by touching an object or surface with the virus on it and then touching their mouth, nose, or eyes. However, this is not considered the main mode of transmission, and the risk of infection from surfaces is generally low.
Situations That Increase Risk
Certain environmental and situational factors significantly elevate the likelihood of contracting COVID-19. Indoor settings pose a much higher risk compared to outdoor environments. Studies indicate that indoor transmission can be substantially higher, with less than 10% of reported global infections occurring outdoors.
Poor ventilation in indoor spaces is a major contributor to increased risk. Inadequately ventilated areas allow viral particles to accumulate in the air, increasing the concentration of the virus people might inhale. This makes it easier for the virus to spread throughout a room.
The World Health Organization highlights specific scenarios that facilitate viral transmission, often referred to as the “Three Cs.” These include crowded places where many people are gathered, close-contact settings where individuals are in close proximity for conversations, and confined and enclosed spaces with poor ventilation. The risk of transmission is particularly high when these three conditions overlap. While individual factors like vaccination status influence susceptibility, these environmental and social circumstances fundamentally shape the potential for exposure.
Can You Get COVID-19 Again?
It is possible to get COVID-19 more than once. Reinfection occurs when an individual recovers from a previous infection and then becomes infected again. This can happen due to the waning of natural immunity acquired from a prior infection. Protection against reinfection can decrease over several months.
The emergence of new SARS-CoV-2 variants also contributes to reinfection. These variants can develop mutations that allow them to evade existing immunity, a process known as immune escape. For instance, the Omicron variant significantly impacted how natural immunity protects against reinfection, reducing protection after a year compared to earlier variants. Although vaccination provides protection, it does not completely eliminate the chance of reinfection.