COVID-19 is an infection caused by the severe acute respiratory syndrome virus
(SARS-CoV-2). This coronavirus was first detected in Wuhan, China in December 2019. On March 11, 2020, the World Health Organization (WHO) declared COVID-19 a pandemic. This pandemic is still in effect and has great implications for travelers in Canada and internationally.
SARS-CoV-2 is mainly transmitted during prolonged close contact between people. The virus is excreted through the respiratory tract of an infected person. It is mainly transmitted by proximity aerosols.
The incubation period is 2 to 14 days after contact with an infected person in their contagious period. The period of contagiousness extends from a few days before and can go up to 10 days after the date of the onset of symptoms. The duration of contagiousness is longer in immunocompromised people.
Most people infected will have mild to moderate respiratory symptoms. However, some people will have a more serious illness that will cause them to be hospitalized. A minority will have to be hospitalized in intensive care and may die. In addition, many patients will have long-term sequelae.
Risk factors for suffering from severe COVID-19 include advanced age, obesity, diabetes, heart and lung disease, cancer, and immunosuppression, among others. Severe COVID-19 cases and deaths can occur at any age, even in the absence of risk factors. Vaccination reduces the risk of serious illness, hospitalization and death.
Variants
As with most viruses, errors sometimes occur randomly during the replication of the genetic material of the SARS-CoV-2 virus. These are mutations. When several mutations modify the properties of the virus, it is a variant of the virus or a new lineage. This phenomenon is common. Variants are being monitored for the impacts they could have on the evolution of the COVID-19 pandemic, including affecting transmissibility, severity, or immune response. They are classified into two categories by the WHO: variants of concern and variants of interest.
As of December 15, 2021, five variants have been classified as variants of concern by the WHO:
| Variant name | Line | Countries where the first samples were recorded | Date of appearance |
|---|---|---|---|
| Alpha | B.1.1.7 | UK | September 2020 |
| Beta | B.1.351 | South Africa | October 2020 |
| Gamma | P.1 | Brazil | January 2021 |
| Delta | B.1.617.2 | Inde | September 2020 |
| Omicron | B.1.1.529 | Many countries | November 2021 |
There are also variants of interest, such as the lambda variant (C.37, first samples recorded in Peru) and the mu variant (B.1.621, first samples recorded in Colombia).
For an up-to-date list of variants, see the WHO website on variants.