Children asymptomatic cases
A report from the Wuhan Children’s Hospital
which located in the outbreak and
worst-hit areas
described the spectrum of SARS-CoV-2 infection in children, it analyzed
171 cases and concluded that most
infected children appear to have a milder clinical course in contrast
with infected adults, and asymptomatic cases(27/171, 15.8%)were more
common[43]. A retrospective study of 2143
pediatric patients infected with SARS-CoV-2 in China come to a similar
conclusion, the majority of the patients were asymptomatic(94, 4.4 %),
mild (1091, 50.9 %), or moderate cases( 831, 38.8 %), totally
accounted for 94.1 % of all cases. It suggests that there are fewer
severe cases but more asymptomatic infections in children compared with
adult patients[44].
Some scholars believe that this is due to less immune dysfunction after
the SARS-CoV-2 infection in children[45-48]. It is very meaningful
that vaccination with the tuberculosis vaccine bacillus Calmette Guerin
(BCG) could dramatically reducing infant deaths from sepsis and
respiratory tract infection (e.g. influenza). BCG has also been proved
to protect mice from influenza virus infection via nonspecific
protection in animal experiment[49]. This is a type of immune memory
phenomenon that is unique to innate immunity after body is infected or
vaccinated and it can induce T cell-independent protection against
secondary infection, we call it “training immunity”[50]. Perhaps
the helpful training immunity in asymptomatic or mild infection children
could contribute to the future evolution of immunotherapy and vaccines
for the SARS-CoV-2. Another speculation of why children were less
sensitive to SARS-CoV-2 was that the function (e.g. binding ability) of
Angiotensin Converting Enzyme-2 (ACE-2) identified as the cell entry
receptor of SARS-CoV-2 in children may be lower than that in
adults[44].