COVID-19 is caused by SARS-CoV-2, a virus that affects the upper and lower respiratory tracts. Most kids who get COVID-19 do not get sick at all, or only feel sick for a short time. But sometimes children who have had COVID-19 can feel unwell for several weeks or months after the infection. They continue to feel exhausted, have shortness of breath, and have trouble doing daily tasks. This is called long COVID, and doctors are trying to understand it and find ways to protect people. In this article, we will explain what can happen when kids get COVID-19, what long COVID is, and what might cause long COVID to happen in a number of infected people.
SARS-CoV-2: A Mean Villain
SARS-CoV-2 is a fairly new, harmful virus that was first observed in December 2019 in Wuhan, China. Like a mean movie villain, it quickly spread around the globe, causing a pandemic. The name of this virus stands for Severe Acute Respiratory Syndrome-CoronaVirus-2, and it causes the disease called COVID-19 (COronaVIrus Disease-2019) . SARS-CoV-2 is one of many coronaviruses that can infect animals and humans. Like most viruses, we cannot see SARS-CoV-2 with a light microscope. However, we can see it under powerful electron microscopes. SARS-CoV-2 and other coronaviruses appear to have spiky proteins covering them, like a crown (corona), which also explains their name.
SARS-CoV-2 is a respiratory virus that infects the upper and lower respiratory tracts. It spreads via droplets when an infected person talks, coughs, or sneezes. The virus can also be transmitted by touching a surface contaminated with the virus and then touching the nose or eyes. So, we can help defeat this virus by practicing good hand hygiene, coughing and sneezing into a tissue, and getting vaccinated when recommended by the local health authority.
What Happens When Children Get COVID-19?
Infection with SARS-CoV-2 causes COVID-19, a respiratory illness that can range from mild symptoms to severe illness and even death. Common symptoms include fever, cough, and difficulty breathing. Most children who are infected with SARS-CoV-2 do not feel sick. However, since COVID-19 is a respiratory disease, some children who do get sick can have awful breathing trouble or more issues like fatigue, headaches, joint pain, an elevated heart rate, and stomachaches .
In addition, some children who are infected with SARS-CoV-2 may develop what is called Multi-system Inflammatory Syndrome affecting Children (MIS-C). This is a rare illness linked to COVID-19. Often, these children recover from SARS-CoV-2 and develop MIS-C a few weeks later. MIS-C can cause inflammation in various organs, like the lungs, kidneys, heart, and liver. Young patients with MIS-C may develop a high fever, feel weak, and appear pale. They may also have an elevated heart rate, trouble breathing, and stomachaches. It is not uncommon for their skin color to change, too. Do not worry, doctors are learning more about MIS-C every day. Together with scientists, doctors will find new ways to save kids from the harm caused by MIS-C.
What Is Long COVID?
Some COVID-19 patients continue to suffer from some COVID symptoms for 2–3 months or more. This means they have developed long COVID. Children with long COVID commonly feel fatigued, and they struggle to do routine tasks . Other common symptoms are loss of smell or taste, headaches, joint pain, and tummy pain. Children who have long COVID may have trouble sleeping at night (insomnia), and during the day they may feel depressed and anxious (Figure 1). You may be wondering whether long COVID is caused by SARS-CoV-2 alone. The answer is no. Currently, there are three possible causes of long COVID. These include the immune system’s “oopsies” (Figure 2A), “nagging” virus that remains in the body  (Figure 2B), and itty-bitty blood clots  (Figure 2C).
The Immune System’s “Oopsies”
The human body has an immune system that is composed of an army of “soldier” cells that are well-trained to recognize and fight off germs. These cells are trained by either the vaccine (if a person is vaccinated) or by the infection itself. Training the immune cells by getting vaccinated is the best and safest way to prevent people from becoming very sick. Normally, trained immune cells will only attack and kill infected cells; that is what they were trained for, after all! However, sometimes the immune cells can accidentally attack healthy cells instead of the infected ones. Oops! When this happens, it can cause the body to feel damaged or have symptoms that can be dangerous and last for many weeks (Figure 2A).
The “Nagging” Virus
One possible cause of long COVID is that the body does not completely clear the virus. The remaining small amount of “nagging” virus contributes to the development of long COVID. Pieces of SARS-CoV-2 can stay in the body for months after recovery . When this happens, the immune system keeps immune cells active to fight the virus, even though the person does not feel sick anymore. This can cause inflammation in the body, which can make it take longer for the person to feel completely better (Figure 2B).
Itty-Bitty Blood Clots
Although COVID-19 is a respiratory disease, SARS-CoV-2 can damage other body systems, too. The circulatory system (the heart and blood vessels) is another system that SARS-CoV-2 can harm. This can lead to the formation of tiny (itty-bitty) blood clots. Blood clot is when the blood in our body gets sticky and forms a lump. This can sometimes happen when we have a cut or an injury to protect our body, but it can also happen in our veins and block the blood flow preventing some organs from getting enough blood. In this case, a doctor may need to give medicine to help dissolve the clot to save the organs from dying off. Thanks to scientists who have created new instruments that can help doctors find these itty-bitty blood clots, doctors can often treat them before they become dangerous (Figure 2C).
In this article, we have told you about COVID-19, a fairly new disease that can affect children and adults. Most children who catch the disease caused by SARS-CoV-2 recover quickly and only have mild symptoms of COVID-19. However, some children can get more serious illnesses, like MIS-C. Thankfully, this disease is becoming rarer. Other children may end up with long-lasting symptoms, which is known as long COVID. If you feel you are not returning to normal a few weeks to 3 months or more after getting COVID-19, talk to your parents or doctor. Doctors and scientists are working around the clock to figure out what causes long COVID and to protect children and grownups from suffering from this rare but serious condition.
Pandemic: ↑ When a disease spreads to a large number of people in many countries worldwide.
Respiratory Virus: ↑ A type of virus that can infect the respiratory system. The respiratory system is the part of the body that helps us breathe.
Upper Respiratory Tract Infection: ↑ Nose and throat infection.
Lower Respiratory Tract Infection: ↑ Infection of the lungs.
Multi-System Inflammatory Syndrome (MIS-C): ↑ A body-wide inflammatory disease that can develop, in rare cases, weeks after initial SARS-CoV-2 infection in children.
Inflammation: ↑ The protective reaction of the body against an infection or an injury, resulting in heat, redness, and swelling.
Long COVID: ↑ When someone who has had COVID-19, even if they did not have severe symptoms, still feels sick for a long time afterward (up to 2 months or more).
Immune System: ↑ The body’s natural defenses.
Conflict of Interest
DB has received a grant from Pfizer to study Long COVID in children.
The remaining author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
 ↑ Huang, C., Wang, Y., Li, X., Ren, L., Zhao, J., Hu, Y., et al. 2020. Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China. Lancet 395, 497–506. doi: 10.1016/S0140-6736(20)30183-5
 ↑ Buonsenso, D., Di Gennaro, L., De Rose, C., Morello, R., D'Ilario, F., Zampino, G., et al. 2022. Long-term outcomes of pediatric infections: from traditional infectious diseases to long Covid. Fut. Microbiol. 17:551–571. doi: 10.2217/fmb-2022-0031
 ↑ Brackel, C., Lap, C. R., Buddingh, E. P., van Houten, M. A., van der Sande, L., Langereis, E. J., et al. 2021. Pediatric long-COVID: An overlooked phenomenon? Pediatr. Pulmonol. 56:2495–2502. doi: 10.1002/ppul.25521
 ↑ Buonsenso, D., Martino, L., Morello, R., Mariani, F., Fearnley, K., and Valentini, P. 2023. Viral persistence in children infected with SARS-CoV-2: current evidence and future research strategies. Lancet Microbe. 4:e745–e756. doi: 10.1016/S2666-5247(23)00115-5
 ↑ Couzin-Frankel, J. 2022. What causes Long Covid? Here are the three leading theories. Science | AAAS. Available online at: https://www.science.org/content/article/what-causes-long-covid-three-leading-theories (accessed June 16, 2022).