Why Children Have the Strongest Immunity to COVID-19
Since the Covid-19 pandemic broke out, through mutations, the virus has generated many variants. The world has gone through many ups and downs as we respond to the pandemic in many ways.
However, there is one group of people who have always been at the right end of the immunity spectrum: the children.
This was one of the few signs of hope throughout the crisis. When people speak of infectious disease, there are usually three major groups at high risk: children, the elderly, and pregnant women.
A special phenomenon emerged throughout the Covid-19 pandemic, however. The elderly had a high mortality rate, adolescents were less affected, and although many children have been exposed to and infected with Covid-19, they only show very mild symptoms, and the mortality rate is very low.
In an article published in the journal Nature in 2021, it was mentioned that there is a group of people who are at the right end of the Covid-19 immunity spectrum: children. Scientists have theorized that children are the least affected by the Covid-19 outbreak, because they have a stronger “innate immune system.” According to Dr. Kawsar Talaat, an infectious disease physician at Johns Hopkins University, one of the few hopes for the pandemic is that children are relatively immune to Covid-19.
Why Are Children Less Prone to Covid-19 Infection Than Adults?
In comparison with adults, children’s immune system has several advantages.
Children have stronger innate immunity. Since the outbreak of the pandemic, researchers have noted that children have greater protection against the virus than adults. Another article published in Nature compared and analyzed the differences in several typical cell groups between children and adults:
Neutrophils are cells in the innate immune system that, when activated, summon immune cells to the area of infection and are the body’s first line of defense against invading pathogens. In children, who were not infected by Covid-19, researchers found that the amount of neutrophils in them exceeded that of adults by 21.85 percent.
After the body is infected by a virus, type 1 and type 2 cytotoxic T cells in the acquired immune system are activated to respond to the specific pathogen, destroy the virus, and create immunological memory. The differences in the amounts of cytotoxic T cells and T lymphocytes between adults and children are not significant, only about 1.12 percent and 3 percent respectively.
An analysis of the numbers of these three types of cells shows that the amount of neutrophils in children is much higher than that in adults, which indicates that children have particularly strong innate immunity.
Children have more active innate immune genes. Once the body is infected with a virus, a large number of immune genes are also activated.
Another report in the journal Nature analyzed a number of immune genes. It discovered that in uninfected adults, their immune genes’ expression quantity is similar to that in children. However, once they are infected, the degrees of activation of some immune genes are not as high as those in children. We’ve selected several of these genes for comparison:
In infected children, the macrophage scavenger receptor 1 gene (MSR1) is activated to a very high degree. In addition, since children’s innate immunity is inherently strong, it would further activate these genes, allowing the body to destroy foreign pathogens more effectively.
There is also the ZEP1 gene, which is a protein that binds to zinc ions and regulates the expression of interferons. These genes are activated to a much higher degree in infected children than in infected adults.
On the one hand, children have a greater number of innate immune cells; on the other hand, their internal genes are more prone to activation. With both internal and external factors, children have a stronger comprehensive ability to fight against virus invasion.
Children fight against the virus more effectively. After Covid-19 infection, the immune cells in children and adults are activated differently.
Neutrophils: In the absence of virus infection, the quantity of neutrophils is already relatively large in teenagers and children under 20 years of age. After virus infection, neutrophils would become activated, and the amount of neutrophils activated in adults aged 20 and above is significantly lower than that in children.
Type 1 and type 2 cytotoxic T cells: After viral infection, the number of activated acquired immune cells become even larger in teenagers and children under the age of 20. And the T cell activation ability decreases significantly with age.
Another study published in the journal Nature found that after viral infection, the CD8 receptors expressed by killer T cells in children are activated to a higher degree than in adults. This means that the immune cells proliferate faster after a foreign virus invasion, thus achieving a stronger defense ability.
Does the Prevalence of Omicron Affect Children?
A Journal of the American Medical Association (JAMA) study analyzed the hospitalizations in children aged 5 to 11 years in 11 US states from January to March 2021, and compared the data with those of children hospitalized with influenza and respiratory syncytial virus during the same period in 2017.
The results showed that the total number of hospitalizations for children infected with Covid-19 did not exceed the number of influenza hospitalizations in the same period in 2017. The numbers of deaths due to Covid-19 and influenza were less than 11 respectively (in this study, the specific number of deaths was not counted if less than 11).
The total length of hospitalization stays for children aged 5 to 11 who had Covid-19 was shorter than that for influenza and respiratory syncytial virus hospitalizations. It is important to note that some children with Covid-19 infection would develop multisystemic inflammatory syndrome (MIS-C), which is uncommon and mostly curable. However, it will still require close monitoring and prompt medical attention, if a child with Covid-19 infection develops symptoms of inflammation of organs and/or tissues.
The most recent data from the American Academy of Pediatrics found that as of April 28, 2022, the hospitalization rate for children with Covid-19 infection is low, with an average hospitalization rate of 0.1 percent to 1.5 percent, and an even lower mortality rate of 0 to 0.02 percent.
Every country has experienced a surge in infections during the Omicron pandemic, and it is difficult to avoid infections in children. Although the overall number of children infected with Covid-19 during the Omicron pandemic has also increased significantly, we can see from the above data that the hospitalization and mortality rates for children are currently still quite low.
Vaccine Protection for Children Under 5?
The Food and Drug Administration (FDA) is currently exploring whether vaccines should be administered to children under the age of 5. So, how much protection do vaccines offer to children?
First of all, there is a lack of clinical data on the effects of vaccines on children. So we don’t know exactly how protective vaccines are for children and what the side effects are.
According to a study of the Pfizer vaccine’s protection in adolescents published in New England Journal of Medicine, the rate of protection against severe illness in adolescents aged 12 to 18 declined significantly between the Delta and Omicron pandemics.
The Pfizer vaccine’s average rate of protection against severe illness in adolescents aged 12 to 18 is 40 percent. This does not meet the 50 percent protection threshold set by previous standards for vaccines. For children, the Pfizer vaccine’s protection rate is 68 percent.
In fact, as long as children have a normal diet, balanced vitamin intake, and adequate exercise, their immune system is already very strong. Therefore, parents should be more cautious when the side effects of vaccines on children are not yet known. It is important to find out if a child has underlying medical conditions or is allergic to vaccines, and this should be part of the consultation with a doctor on childhood vaccinations.
Xiaoxu Sean Lin, Ph.D., former US Army Officer and microbiologist, is a political analyst and commentator.