About the common cold, flu & COVID-19
While the common cold, flu, and COVID-19 are all contagious respiratory illnesses, they are caused by different viruses. A cold is typically mild and gradual, while the flu hits suddenly and hard. COVID-19 can range from going unnoticed to mild to extremely severe.
Common Cold: Symptoms usually appear 1–3 days after exposure. It is mostly caused by rhinoviruses.
Flu: Symptoms typically develop 1–4 days after infection. Caused by influenza A and B viruses.
COVID-19: Symptoms can appear 2–14 days after exposure, though the average is about 5 days. COVID-19 is generally more contagious than the flu.
How They Spread
All three viruses spread through similar respiratory mechanisms, but they differ in how effectively they use each route.
Primary Transmission Routes
Respiratory Particles (Aerosols and Droplets): All three are primarily spread through particles expelled when an infected person breathes, talks, coughs, or sneezes.
Large Droplets: These are heavier and typically fall to the ground within roughly 2 metres (6 feet).
Small Particles (Aerosols): These are lighter and can linger in the air for minutes or even hours, potentially traveling further than 2 metres, especially in poorly ventilated indoor spaces.
Surface Contact: You can catch these viruses by touching a surface (like a doorknob or phone) contaminated with the virus and then touching your eyes, nose, or mouth. While common for the cold and flu, health experts at the Mayo Clinic note that this risk is relatively low for COVID-19.
Key Differences in Spread
Contagiousness: COVID-19 is generally considered more contagious than the seasonal flu and the common cold.
Super-spreading: COVID-19 is more likely to cause "super-spreading events," where one infected person transmits the virus to many others simultaneously.
Asymptomatic Spread: Both COVID-19 and the flu can be spread by people who have no symptoms or who haven't started showing symptoms yet. This is a major driver for COVID-19, which has a longer incubation period (up to 14 days) than the flu (1–4 days).
Environmental Factors: All three viruses tend to survive better and spread more easily in cool, low-humidity environments, which is why cases often peak during winter months when people spend more time indoors.