A first-of-a-kind study found clues on why pediatric cases of COVID-19 are milder than adults. The results highlighted the intensity of innate immunity, which might be responsible for robust immune responses in children.
The reasons behind the mild COVID-19 in pediatric cases were investigated by scientists at Children's Hospital at Montefiore (CHAM), Yale University, and Albert Einstein College of Medicine, a US private medical school. They found notable differences in the immune responses between children and adults with COVID-19. While adults might be better with adaptive immunity, children were likely more effective in fighting SARS-CoV-2 due to their innate immunity. They published their findings in the journal Science Translational Medicine.
The COVID-19 Data on Different Age Groups
In infectious diseases, there are population groups usually considered at risk of severe outcomes and mortality. These groups include children, pregnant women, elderlies, people with chronic conditions, and people with weakened immune systems. As such, health experts advise these groups to take extra precautions in the current pandemic.
According to Statista, a German portal for statistics, the fatality rate of COVID-19 was higher among older adults and elderlies in the early stages of the pandemic. In a report by the Chinese Center for Disease Control and Prevention, out of 44,672 confirmed cases of COVID-19 in Mainland China, the highest fatality rate was among people aged 80 years and older at 14.8%, as of February 11, 2020. It was followed by 8% among aged 70 to 79 years, 3.6% among aged 60 to 69 years, 1.3% among aged 50 to 59 years, 0.4% among aged 40 to 49 years, 0.2% among aged 30 to 39 years, 0.2 among aged 20 to 29 years, and 0.2% among aged 10 to 19 years. The figures showed that the fatality rate increases with age.
On the other hand, research and economist Andreas Backhaus suggested the differences of COVID-19 in age groups. In the data reviewed by Backhaus, 0.8% of cases in South Korea and 0.5% of cases in Italy were aged zero to nine years. While 5% of cases in South Korea and 1.1% of cases in Italy were aged 10 to 19 years.
Other case percentages in South Korea were 29.9% among aged 20 to 29 years, 10.7% among aged 30 to 39 years, 13.78% among aged 40 to 49 years, 18.9% among aged 50 to 59 years, 12.3% among aged 60 to 69 years, 5.7% among aged 70 to 79 years, and 3% among aged 80 and older. In Italy, the other rates were 3.7% among aged 20 to 29 years, 5.9% among aged 30 to 39 years, 11.1% among aged 40 to 49 years, 18.1% among aged 50 to 59 years, 18.3% among aged 60 to 69 years, 22.2% among aged 70 to 79 years, and 19.1% among aged 80 and older.
Children's Immune System May Be Robust against SARS-CoV-2
Normally, young adults have the best immune system across all ages. Their immune systems are fully matured and already encountered many infections early on. So, they are likely to be protected from different pathogens and likely to recover faster, compared to children and older adults. However, there is an unusual trend when it comes to COVID-19. Children are less likely to suffer from serious complications and mortality due to SARS-CoV-2. Even though there are reported cases of COVID-19 pediatric deaths, the numbers are significantly low when compared to other age groups.
Scientists from three institutions joined forces to determine the reason behind that trend. They investigated both pediatric and adult patients with COVID-19. They examined all relevant factors to answer the question: why were children unlikely to get seriously ill from the disease? Their investigation showed that the immune system of children acted differently than adults. Even with premature immune systems, pediatric patients had a higher chance of fighting the coronavirus.
"Our findings suggest that children with COVID-19 do better than adults because their stronger innate immunity protects them against SARS-CoV-2, the novel coronavirus that causes the disease," said Dr. Betsy Herold, a senior author of the study and chief of infectious diseases at Einstein.
In the study, the team examined the data of 60 adult COVID-19 patients and 65 pediatric COVID-19 patients, who were aged younger than 24 years. The patients have been hospitalized at CHAM and Montefiore Health System from March 13 to May 17, 2020. Out of all pediatric patients, 20 developed the novel multi-system inflammatory syndrome or MIS-C, a complication of COVID-19. Blood samples of patients were tested for several immune cell types, antibody activity, and inflammatory proteins called cytokines.
The outcomes of patients were assessed as well. Pediatric patients fared better wherein only 8% of them were on mechanical ventilation, compared to 37% of adult patients. Only 3% of pediatric patients died from the illness, compared to 28% of adult patients. No pediatric patients who developed MIS-C died from the complication or COVID-19.
The scientists suggested that children have better innate immunity than adults. The human body's immune system is mainly divided into two: innate and adaptive. The former is very old in terms of evolution when compared to adaptive. Innate immunity is the immediate response to any unfriendly matter that enters the body. It is a general form of immune response, as opposed to the specialized response of adaptive immunity.
Since the immune system of children is still developing, their body has better innate immunity than adaptive. Once the coronavirus enters their body, innate immune cells will respond quickly. Due to the majority of immune cells being innate, the virus may not successfully establish itself. And without the developed adaptive immunity, certain chemical signals are not yet available that may induce serious, system-wide inflammation.
The robust innate immunity was evident in the high levels of specific cytokines linked to innate immune responses. Pediatric patients had higher concentrations of interleukin-17A. The cytokine interfered with the progression of COVID-19. Thus, most pediatric patients had better outcomes compared to older people. And when it comes to antibodies, adult patients produced more antibodies than pediatric patients. But the adaptive immunity in adults caused their bodies to overreact, which triggered inflammation and serious complications. Researchers suggested therapies that could boost innate immunity might help COVID-19 patients.