Children are immune prepared for SARS-CoV-2

At least 30 new diseases have emerged in the last 20 years and now together threaten the health of hundreds of millions of people. For many of these diseases, there is no treatment, cure, or vaccine. While most of these diseases are dangerous to children, especially those younger than five years old, the novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2),  seems to spare most of them. Though they can still contract the virus, most infections are mild, and severe COVID-19 disease in children is rare.

A new study by researchers at the Bambino Gesù Children’s Hospital in Rome sheds light on why most children are spared by COVID-19. Children are more vulnerable to other infections, including influenza, pneumonia, viral gastroenteritis, and measles, among others. The important question is, why are children less susceptible to COVID-19 compared with adults?

Children and COVID-19

The SARS-CoV-2 infection first emerged in Wuhan City, Hubei Province, China in early December 2019. It was a day before New Year’s Day that a cluster of 27 patients with the pneumonia-like illness was reported as “the treatment of pneumonia of unknown cause” to various hospitals in the city.

The immune system of children: the key to understanding SARS-CoV-2 susceptibility?. The Lancet. Image Credit: Mongkolchon Akesin . Shutterstock

After a couple of weeks, the virus spread across China, and by February and March, it had conquered Europe, with Italy then Spain taking the hardest hit. Since then, the virus has spread to 187 countries and territories and infected more than 3.84 million people. COVID-19 has killed more than 269,000 people.

Most of the cases, however, are among adults, while most deaths occur in older adults. In a previous study by Chinese researchers, they found that compared to younger patients, middle-aged and older adults are far more likely to suffer symptoms, placed in intensive care units, and even to die. In the study in a subset of 24 people who died due to the illness, the projected chance of COVID-19 cases is 13 percent for patients who are 80 years old and above, compared to just 0.15 percent in people who are in their 30s. For those who were younger than 20, the fatality rate was 0 percent.

However, in other countries, cases of children dying from coronavirus disease have been reported. Though the rate is low, it may provide an insight into why some children are vulnerable, and others are spared.

Immune preparedness of children

During the first months of life, maternal antibodies help protect children from pathogens that were previously contracted. Although sanitation practices and the development of vaccines have been established to protect children from deadly infections, all microorganisms are new to the child.

During the first year of life, the diseases the child encounter serve to build the pool of memory T and B cells to avoid reinfection. After, the children’s immune systems are prepared to fight off pathogens as they grow up, which may be lacking in people who are 70 years old and above. Aging may take a toll on the immune system, working as less efficiently as before.

While innate immunity and the potent T cells play significant roles in warding off infections, antibodies may help fight the pathogen. For instance, past outbreaks such as the SARS in 2002, Ebola in 2014, and the H1N1 in 2009, convalescent plasma containing antibodies from recovered patients was utilized to treat patients at the early stage of the illness.

Children have undergone immune preparedness, which played a pivotal role in protecting the novel coronavirus or SARS-CoV-2. First, children have natural antibodies that stave off the virus, even if these antibodies were formed in response to other infections.

Next, children can rapidly produce natural antibodies with broad reactivity, and as a novel pathogen challenges the immune system, immune cells can provide a raid reaction, which allows for the secretion of antibodies. In infants and children, memory B cells or MBCs are highly adaptable to new antigens. In contrast, in older adults, the MBCs can recognize their targets but are incapable of adapting to new antigens.

To test their theory, the researchers have started a prospective study. The preliminary results of the study suggest that in children, an early polyclonal B cell response help produce a substantial number of plasmablasts, which are of IgM isotype.

“With aging, malnutrition, immunosuppression, and co-morbid states, our immune system loses the ability to adapt to novelty.  Although vaccines are the way forward, in emergency situations such as the   COVID-19   pandemic, the investigation and use of immune tools that nature has endowed to children might improve management outcomes,” the researchers wrote in the paper.

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