Overview of COVID-19

What are the common symptoms of COVID-19 infection?

COVID-19 is the disease caused by the SARS-CoV-2 coronavirus. Some people who become infected become seriously ill. Others experience mild symptoms, and some never show symptoms. Symptoms can include fever, cough, shortness of breath, fatigue, a stuffy or runny nose, loss of sense of smell and taste, diarrhea, and headache. The median time between infection and the appearance of symptoms is about five days (Lauer et al. 2020), although this period may be longer in children (Zhu et al. 2020). The time between infection and appearance of symptoms ranges from 2 to 14 days, and as a result, contagious individuals can spread the virus before they realize they are infected.

In general, COVID-19 illness appears to be less severe in children under five than in adults and older children, although children who have chronic diseases or pre-existing conditions, such as obesity or chronic lung disease, may be at a higher risk for severe COVID-19 requiring hospitalization (Kim et al. 2020). The risk of COVID-19-associated hospitalization may be higher for “Hispanic/Latino” children and “non-Hispanic black” children (Kim et al. 2020). There have also been cases of children developing a rare but serious condition called multisystem inflammatory syndrome as a result of COVID-19. Although children represent a relatively small proportion of global COVID-19 cases (possibly due in part to lower testing rates), generally have milder symptoms, and are more likely to be asymptomatic, the potential for serious illness in children cannot be dismissed.

How is the virus that causes COVID-19 transmitted?

There are three ways the virus that causes COVID-19 can be transmitted, both by people who are symptomatic as well as those without symptoms: close contact transmission, long-range transmission, and transmission from contaminated surfaces.

Close-contact transmission

When infectious people exhale, speak, cough, sneeze, or sing, they produce large virus-laden droplets that can land in another person’s mouth, nose, or eyes, as well as smaller virus-laden aerosols that can be inhaled directly into another person’s respiratory tract. Droplet and aerosol transmission can be minimized by physical distancing (at least six feet apart whenever possible for high school students and adults and at least three feet apart for K-8 students), wearing face masks, and staying home when feeling sick. There is definitive evidence that wearing a mask reduces spread of COVID-19, and it should be a part of return to school.

Long-range transmission

Aerosols that are produced when an infected person exhales, speaks, sneezes, or coughs and that contain the COVID-19 virus can also stay aloft and travel in the airflow around a room (World Health Organization 2020). This airborne virus can remain suspended in the air indoors for more than an hour and infect people who were not physically close to the sick person. In addition to physical distancing, wearing masks, and staying home when sick, long-range transmission can be reduced by increasing outdoor air ventilation, which dilutes the concentration of airborne virus, or by filtering air recirculating in a room or building.

Touching a contaminated surface and then touching your face

Surfaces like desks, tables, playground equipment, or water fountains can be contaminated if an infected person coughs or sneezes directly on them, or into their hands and then touches the surface before washing or sanitizing his or her hands. Others may then touch the surface and touch their nose, mouth, or eyes without washing or sanitizing their hands first. The virus can last on different surfaces for varying amounts of time, although risk of transmission reduces as time passes. Transmission by contaminated surfaces can be reduced through frequent cleaning and disinfection of commonly-touched objects, using automatic or touchless alternatives (e.g., automatic doors), and frequent hand-washing.

Transmission rates among children

It is important to note the difference between infection rates - the proportion of positive cases in a population - and transmission rates - the rate at which the virus is spread from an infected person to others, or the number of people to whom the virus has spread from one person. Each individual who is infected may spread the virus to others at a different rate. Differences in transmission rates may stem from biological factors such as the amount of virus in a person’s body, and social and behavioral variables, such as the number of people an individual comes into physical contact with, the nature of that contact, and adherence to basic transmission prevention safety measures, among others.

Our current understanding of COVID-19 suggests that children under ten are less likely to transmit the virus to older children and adults (Wilson 2020; Boast et al. 2020; Boulad et al. 2020; Li et al. 2020; Lee and Raszka 2020; Munro and Faust 2020; Ludvigsson 2020b; Ludvigsson 2020a; World Health Organization 2020), although this continues to perplex epidemiologists and infectious disease experts because young children are significant spreaders of other respiratorily-transmitted viruses. It is not entirely clear how the results of studies on COVID-19 transmission by and among children who have not been in school apply to contexts in which children do return to their usual in-person school and other activities. The evidence is only emerging regarding the age- and developmental level-related factors that may contribute to transmission. As the evidence matures, we will continue to review this issue.

What factors determine COVID-19 risk?

Risk for COVID-19 infection depends on age (see above), gender, immune status, pre-existing conditions, especially obesity and diabetes, race, class, genetics, housing, and work-related exposures; the local health care system’s capacity; and how well available treatments work. Another important factor to consider is a person’s tolerance for risk. Some are willing to take on more risk, while others try to avoid risk as much as possible.

Our current understanding of COVID-19 suggests that children are less likely to contract the virus. Children (particularly school-age children below the age of five) appear to be at lower risk of severe COVID-19 than adults and older children.