Transmission, pathogenesis, replication of SARS-CoV-2 (COVID-19)


SARS-CoV-2 is the virus that causes COVID-19, a respiratory disease that has become a global pandemic. Understanding how the virus spreads among people is crucial for preventing and controlling its transmission. According to the current scientific evidence, there are three main modes of transmission of SARS-CoV-2:

  • Droplet transmission: This occurs when respiratory droplets (as produced when an infected person coughs or sneezes) are ingested or inhaled by individuals in close proximity (within 6 feet). Respiratory droplets are larger than 5 micrometers in diameter and can carry virus particles. They can also land on exposed mucous membranes (such as the mouth, nose, or eyes) or on surfaces and objects contaminated with the virus.
  • Contact transmission: This occurs when a person touches a surface or object contaminated with the virus and then touches their own mucous membranes. The virus can survive on different materials for varying periods of time, depending on the environmental conditions. Contact transmission can be prevented by frequent hand washing and disinfection of high-touch surfaces.
  • Aerosol transmission: This occurs when respiratory droplets mix into the air, forming aerosols, and cause infection while inhaling a high dose of aerosols into the lungs in a relatively closed environment. Aerosols are smaller than 5 micrometers in diameter and can remain suspended in the air for minutes to hours. They can travel farther than 6 feet and accumulate in poorly ventilated spaces. Aerosol transmission can be reduced by wearing masks, improving ventilation, and avoiding crowded indoor settings.

These modes of transmission are not mutually exclusive and can occur simultaneously. The risk of infection depends on several factors, such as the amount and duration of exposure, the viral load of the source, the susceptibility of the host, and the environmental conditions.

In addition to these modes of transmission, there is some evidence that SARS-CoV-2 can also be transmitted through other routes, such as fecal-oral transmission, blood transfusion, vertical transmission from mother to child, and animal-to-human transmission. However, these routes are considered less common and require further investigation.