Discussion
In January of 2020, Zhejiang province activated its Level 1 emergency
reaction to the COVID-19 pandemic. Several NPIs were adopted for the
purpose of suppressing or mitigating the virus spread. Respiratory tract
virus infection in children has always been the focus of attention at
home and abroad. Tremendous efforts were made to minimize common
childhood respiratory virus prevalence apart from COVID-19 containment
[2,12,13]. Herein, virus-positive sample numbers increased by 7.2%
compared to before COVID-19. The detection percentages were relatively
unaffected; this increase in numbers may be the result of a combination
of factors, including a presumed decline in population immunity and a
loosening of COVID-19 limitations.
More specifically, we found that the test positivity rate is extremely
high over the period of the COVID-19 outbreak; the strongest
contribution is provided by RSV, whose prevalence has experienced a
significant increase, consistent with results described by reports from
Australia[13,14], and New Zealand, likely corresponding to relaxing
NPIs. These phenomena may be associated with the concept of “immunity
debt”[15,16], emphasizing the necessity of recognizing NPIs as a
double-edged sword; this highlights the criticality of active and
ongoing epidemiological surveillance and timely adjustment of
immunization approaches. The epidemiological trend of RSV infection in
children had undergone a significant alternation before and after
COVID-19 in East China. A significant reduction in the ADV, Flu B, and
PIV-2 and -3 during
COVID-19
was identified, which was in the same line with observations from other
reports[17,18].
Herein, children between the ages of 1-12 months are the most
susceptible to respiratory viruses, particularly RSV, both prior to and
throughout COVID-19; surprisingly, compared to before COVID-19,
respiratory infection prevalence was almost higher after COVID-19 in
this age group, where it decreased significantly in other age groups.
When a virus infects a host, the immune system is activated to fight the
pathogenic microorganism[19]. In children under one year old,
lacking complete immune memory and decreased innate and adaptive
immunity due to the immature immune system may be liable to their
respiratory-virus vulnerability, with NPIs having little
influence[20]. Nevertheless, neonates receiving massive passive
antibodies from mothers and older children whose immune systems are more
thoroughly developed may benefit to a great extent from NPIs
implementation in their protection against respiratory viral infections.
This study showed that some respiratory viruses had obvious seasonality,
and the detection rates of RSV and Flu A were high in winter. During
COVID-19, PIV-3 was detected mainly in autumn and winter, while before
COVID-19, PIV-3 was detected mainly in summer, followed by spring. Since
Flu is mainly transmitted by droplets and contact, the prevention and
control measures taken in the early stage of the novel coronavirus
outbreak were just in spring and summer, basically the same as those
taken for flu prevention and control. It can effectively block the
transmission of Flu. Nevertheless, at the beginning of the fall semester
in September 2020, in the light of the Chinese domestic COVID-19
outbreak in remission, people generally went back to normal work and
life in low-risk areas, like those prior to COVID-19; this may clarify
the spike in PIV-3 infection in summer of 2020, consistent with relevant
research results[21].
This study has some drawbacks as it is only a single-center study;
besides conducting a retrospective analysis and collecting the data of
children admitted to our hospital, hence the other factors which may
relate to respiratory virus infection were not analyzed.
In conclusion, RSV infection is the most frequent respiratory tract
infection, with significant differences in distribution between
different ages and different seasons. COVID-19 prevention and control
measures can effectively contain ADV, Flu A and B, and PIV1, 2, and 3
transmissions. Herein, the respiratory virus was detected and analyzed
in hospitalized children with acute respiratory tract infection to
provide evidence for the clinical diagnosis and treatment of respiratory
tract virus infection during the epidemic period.