Introduction
The opinion that the infant immune system is weak compared to the adult
immune system isn’t quite fair. Early at the start of the COVID-19
pandemic, kids’ parents and doctors have been scared about the
consequences of infection and disoriented about the steps to be taken if
their children test positive or are infected with COVID-19. With other
viruses, adults have the advantage of prior exposure. Through prior
infection or vaccination, their immune systems have been trained to
contend with similar pathogens. The novelty of SARS-CoV-2 showed that
children have an innate immunity against viral infections.
COVID-19 affects children and adults differently
Young children account for only a small percentage of COVID-19
infections—a trend that initially puzzled clinicians and researchers.
Moreover, children are highly adapted—and very well-equipped—to
respond to new viruses, and are most likely to experience mild or
asymptomatic illness. On the other hand, kids who develop COVID-19
symptoms and antibodies specific to SARS-CoV-2 may not test positive on
RT-PCR testing.
Children better than adults combat SARS-CoV-2
There is no clear evidence of age-related differences in ACE2 expression
in the nose and lungs between both children and adults since scientists
who measured the viral load in people’s upper airways have seen no clear
difference between children and adults. On the other hand, children with
more exposure to coronavirus common cold with the existence of already
protective antibodies to lock on to the pandemic coronavirus might not
be a clue for better combating this novel virus. But the evidence
suggests that adults also have this immunity. In eminently, these
’cross-reactive’ antibodies don’t offer any special protection against
SARS-CoV-2 infections.
Innate Immunity in Children is Well-trained
Research suggests that children have more robust innate immune systems
than adults because of the numerous respiratory infections experienced
within their first few years of life, which may prime their immune
systems for subsequent attacks (trained non-specific immunity). A
growing body of evidence suggests that the innate immune systems of
children usually successfully prevent the virus from multiplying.
Pillars of Innate Immunity in Children
The existence of potent dendritic cells and macrophages which are
embedded and lining the nose and throat in children are prominent and
represent a strong mucosal immunity that frequently encounters new
viruses. These alert cells start to release proteins called
chemokine-like interferons, which help to coordinate the body’s immune
response. Researchers declare that SARS-CoV-2 infected children have
lower levels of inflammatory monocytes, which act to bridge between
innate and adaptive immune responses. On the other hand, the presence of
higher levels of innate lymphoid cells in children is prominent. These
cells represent early line defense with a significant ability to
regulate the innate and adaptive immune responses via early antibody
response. In essence, other studies found higher levels of activated
neutrophils, the front-line immune response cells to new or novel
invaders, among infected children with SARS-CoV-2 compared with adults.
Strikingly, pediatric hematologists found that children are less prone
to clots forming in blood vessels, which could offer some protection
after inflammation and tissue damage. The major hallmark of COVID-19 is
the systemic inflammatory immune response characterized by a cytokine
storm. It is marked by elevated levels of inflammatory cytokines, mainly
interleukin-6 (IL-6), IL-8, IL-10, tumor necrosis factor-α (TNF-α), and
interferon-γ (IFN-γ). IL-6 is found to be significantly associated with
higher mortality. The role of IL-6 as a pleiotropic cytokine, executing
both pro- and anti-inflammatory activities is well documented. Studies
revealed that a cytokine storm is less likely to occur in children,
indicated by low circulating IL-6, which is the cornerstone of COVID-19
progression initiated by the aggressive inflammatory cascade in adults.
Immunity in children vs. adults
Children’s immune response to SARS-CoV-2 infection is an early
initiative with a low immunological tone, to prevent an overactive
immune system and to rapidly repair damage to the lungs. In contrast,
stormy waves are seen in adults, with exaggerated and overactive
immunity, and with serious sequelae. Therefore, children who are at high
risk of contracting SARS-CoV-2 tend to have pre-existing medical
conditions. Indeed, studies have found that 30–70% of children
hospitalized with COVID-19 had underlying conditions that increase their
risks, including Down syndrome, obesity, lung disease, diabetes, and
immune deficiency. Premature babies are also at higher risk, as are
children who have undergone cancer treatment.
Multisystem inflammatory syndrome (MIS-C) in children
In April 2022 first case of MIS-C was diagnosed among infected children
with SARS-CoV-2 in the United States and the United Kingdom. The exact
cause of MIS-C remains unknown; researchers suggest that viral particles
may leak from the gut into the bloodstream, causing a systemic
inflammatory reaction throughout the body. The symptoms usually appear
between two and six weeks after COVID-19 infection, In spite majority
being asymptomatic or with mild symptoms but children with MIS-C have
antibodies to the SARS-CoV-2 virus. Despite being uncommon, it can have
serious consequences in infants and children, but it can make some
children very ill and in need of urgent care. The syndrome is associated
with a hyper-inflammatory immune process with severe extra-pulmonary
organ dysfunction, particularly in the cardiovascular system.
In conclusion, Kids’ innate immune response against SARS-CoV-2 infection
is early initiative calm with low immunological tone to prevent an
overactive immunity and with rapidly repair damage to the lungs in
contrast to stormy waves in adults. Kids are at much lower risk of
Covid-19 infection and sequels and they are still winning the battle
against Covid-19 with their innate immunity. SARS-CoV-2 typically causes
less severe illness and fewer deaths in children compared to adults.
Even so, children and adolescents remain susceptible to SARS-CoV-2
infection and may transmit the virus to others. To protect children,
right now, the World Health Organization (WHO) has approved some
COVID-19 vaccines for children over the age of 6 months old.
CONFLICT OF INTEREST
The author declare that he have no conflicts of interest.
GRANTS SUPPORT
The study is not supported by any grants or funds from any sources.