COVID-19 is the disease caused by SARS-CoV-2, the new strain of coronavirus that has not been previously identified in humans. It is responsible for the coronavirus outbreak that apparently started in Wuhan, China, in December 2019, and was officially declared a pandemic in March 2020. Although most of the time, symptoms are mild, it can also cause death, and infected persons can pass it on to someone who may experience a more severe form of the disease. The elderly and those with pre-existing conditions are particularly vulnerable to severe COVID-19. Since the pandemic started, over 250 million cases have been confirmed worldwide, including over 5 million deaths, making this one of the 10 deadliest pandemics in the history of mankind. Many variants of the disease have been identified, including the highly contagious Delta variant, leading to numerous, repeated surges and outbreaks around the world. COVID-19 is the disease entity responsible for the ongoing pandemic that officially began in December 2019 in Wuhan, China. Since the pandemic started, over 250 million cases have been confirmed worldwide, including over 5 million deaths, making this one of the 10 deadliest pandemics in the history of mankind.
Last Updated: February 21, 2024

COVID-19 is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). It is related to SARS-CoV-1, which caused the original SARS epidemic of 2002-2004. People are infectious as early as three days before symptoms manifest, and up to 10 days after symptoms have started. This is the reason why quarantine periods last for at least 10 days and must begin after potential exposure to the virus has been determined. Transmission of COVID-19 is primarily respiratory; that is, one becomes infected when one inhales the virus. How this happens, however, has been a controversial topic. Originally, it was believed that the main mode of transmission is through droplets, which was defined as such: People become infected when they are in close contact with someone who has the virus, and whose droplets—virus-containing particles produced when a person talks, sings, coughs, or even just breathes—come into contact with the uninfected person’s mucous membranes (the linings of the eyes or mouth) or are inhaled by that person. These droplets supposedly do not float in the air for too long and quickly fall to the ground. Through this mode of transmission, close contact is a prerequisite for infection. However, it has become increasingly recognized that airborne or aerosol transmission appears to be the dominant mode of transmission. Unlike droplets, aerosols are extremely small and light, virus-containing particles that can stay suspended in the air for a considerable time. In indoor, poorly ventilated spaces, aerosols can stay suspended in the air and be inhaled by an uninfected person even if the infected person is no longer around. As such, COVID-19 is now considered to be transmitted not only through close contact with infected individuals, but also in crowded, poorly ventilated, and enclosed settings (which can include air-conditioned indoor places). Another major cause of transmission is asymptomatic transmission. In some cases, people may be infected with the virus, but manifest no symptoms throughout the duration of illness; however, they can still transmit the virus to other people. This has been a major contributing factor to the difficulty of curbing the spread of infections worldwide. The risk of outdoor transmission remains low, which has led to the growing recognition of outdoor spaces (e.g. outdoor dining in restaurants, public parks, outdoor sports activities) as a vital component of daily living. Fomite transmission—or infection that occurs when one touches a surface that supposedly contains infected droplets, and subsequently touches one’s eyes, nose, or mouth—remains theoretical, difficult to establish, and insignificant. There is no evidence that COVID-19 is transmitted mother-to-child (or intrauterine during pregnancy), through breastfeeding, food or drinking water, or vectors like mosquitoes.

While primarily perceived as a respiratory disease, COVID-19 can apparently affect many different organ systems. Thus, its signs and symptoms have also been varied. The duration of illness is usually within the period of 14 days. In most people, the disease manifests like a respiratory disease—meaning, cough, colds, runny nose, itchy or sore throat, fever, headache, muscle aches, and/or fatigue. However, notable symptoms have also included the loss of (or even just an altered) sense of smell and/or taste, diarrhea, and vomiting. Many people experience only a mild course of illness; however, in the minority of cases, the illness progresses and causes more serious complications. These can include pneumonia and respiratory failure (manifesting mainly as difficulty in breathing), heart problems including heart attacks, and blood clots in the brain or lungs (including embolisms and strokes). These can all be fatal. People more at risk of developing a worse course of disease include the elderly, the immunocompromised, or those with co-morbidities, which includes a wide spectrum of conditions such as asthma, allergic rhinitis, respiratory allergies, diabetes, hypertension, obesity, autoimmune disorders, infectious diseases like HIV, and many diseases of the kidney, liver, heart, blood, and lungs. A subset of infected people will experience no symptoms—otherwise known as asymptomatic disease. Another subset of infected people will experience “Long COVID,” where they experience symptoms that last for a longer period of time, far beyond what most people experience. There have been many reports of previously infected people who continue to experience symptoms that range from chronic or recurrent fatigue, shortness of breath, prolonged distortions to the senses of smell and taste, or even cognitive dysfunction such as memory lapses, “brain fog” (or inability to concentrate), and changes in sleep or mood. Long COVID continues to be a subject of evolving study.

COVID-19 can be diagnosed through swab tests: RT-PCR (more accurate but more expensive and may take 1-3 days depending on the laboratory) or antigen tests (cheaper, faster, better used by symptomatic people, and accurate only within a certain number of days since symptom onset). Depending on the severity of the infection, a health care provider may request other diagnostics. Most of the time, COVID-19 will resolve on its own with rest and supportive home care. Those who are in home or facility quarantine should drink a lot of fluids and be monitored for more serious symptoms. Severe cases require more vigilant monitoring and if necessary, oxygen support and other interventions. The important measure is always to initiate isolation of an individual once potential exposure has been determined, and to undertake testing as soon as possible.

1. Because COVID-19 is airborne, ventilation is key to prevent it. Always choose open, well-ventilated spaces over closed ones. Open a window if indoors, or when in vehicles with other people. 2. Get vaccinated when a vaccine is available to you. Get in touch with your local government to schedule your vaccination if you haven’t done so already. 3. Stay at least 1 meter apart from others, even if they don’t appear to be sick. 4. Wear a properly fitted mask when physical distancing is not possible or when in poorly ventilated settings. Double-masking with a surgical mask over a cloth mask is now recommended in such settings. 5. Practice proper handwashing with soap and water. 6. Isolate yourself if you are experiencing any symptoms, especially fever and/or cough.
Last Updated: February 21, 2024