Influenza versus the common cold—what’s the difference?

Viruses are spread from person to person through airborne droplets that are sneezed out or coughed up by an infected person. In some cases, the viruses can be spread when a person touches an infected surface (e.g., doorknobs, countertops, telephones) and then touches his or her nose, mouth, or eyes. As such, these illnesses are most easily spread in crowded conditions such as schools.

Influenza is commonly referred to as "the flu." Between October and March each year, between 10 and 40 per cent of people are stricken with influenza. Although most people recover fully, the flu causes approximately 7,000 deaths annually in Canada, mostly among high-risk populations (people with other medical conditions or weakened immune systems, the elderly, or very young children). There are three types of influenza viruses: A, B and C. Type A influenza causes the most serious problems in humans.

There are over 200 different known cold viruses, but most colds (30-40 per cent) are caused by rhinoviruses. In Canada, the peak times for colds are at the start of school in the fall, in mid-winter, and again in early spring. Children catch approximately eight colds per year, adults catch roughly four per year, and seniors about two per year.

People infected with an influenza or cold virus become contagious 24 hours after the virus enters the body (often before symptoms appear). Adults remain infectious (can spread the virus to others) for about 6 days, and children remain infectious for up to 10 days.