COVID-19 pandemic-altered epidemiology of respiratory syncytial virus
and human metapneumovirus infections in young children
Tomohiro Udagawa1, Mari Okada1,
Ryuichi Nakagawa1, Haruna Yokoyama1,
Tomoyuki Kato2,4, Maki Furuya3,
Hayato Sakaguchi3,4, Masayuki
Nagasawa1,4*
Department of Pediatrics1, Department of
Pharmacy2, Department of
Laboratory3, Department of Infection
Control4,
Musashino Red Cross Hospital, 1-26-1, Kyonan-cho Musashino-city, Tokyo,
180-8610, Japan
Key word:
COVID-19, viral interference, respiratory syncytial virus,
metapneumovirus,
*Author for correspondence
Masayuki Nagasawa, PhD., MD.
Department of Pediatrics, Musashino Red Cross Hospital
1-26-1, Kyonan-cho, Musashino-city, Tokyo 180-8610, Japan
Tel: +81 422 32 3111
Fax: +81 422 32 9551
E-mail: masayukin@musashino.jrc.or.jp
Correspondence:
Respiratory syncytial virus (RSV) and human metapneumovirus (hMPV) are
closely related viruses belonging to pneumovirinae subfamily and cause
bronchiolitis and pneumoniae in infants and young children, resulting in
hospitalization, which becomes a major health problem in pediatric
care.1,
2 To evaluate the impact of the COVID-19
pandemic on the epidemiology of these viral infections, we investigated
and compared the epidemic patterns of RSV and hMPV infections in
children admitted and diagnosed at our hospital before and after
COVID-19 pandemic. The pathogenic diagnosis was made by antigen test
before 2020 and by Filmarray respiratory panelĀ® (ver2.1) test
thereafter.
In the reports so far, the epidemics of both virus infections have not
completely overlapped in Japan3,
4, and the epidemic peaks of both
infections in our hospital from 2015 to 2019 did not overlap as well as
shown in Figure 1. These phenomena are referred to as social viral
interference and have been mentioned in several viral
infections.5-7 COVID-19,
which emerged at the end of 2019, quickly spread around the world and
became a pandemic.8,
9 Japan also implemented a social
lockdown from April to May 2020. As a result, social activity
restrictions continued, and no epidemics of RSV or hMPV were observed in
2020. After that, a large-scale epidemic of RSV was seen in the summer
of 2021 due to the easing of restrictions on social activities and
movements and the reopening of nursery schools, but no hMPV epidemic was
observed. In 2022 and 2023, epidemics of both RSV and hMPV were seen.
Interestingly, both outbreaks occurred around the same time, unlike
before the COVID-19 pandemic (Figure1). More interestingly, when
comparing the age distribution of infected children, the age
distribution in post-COVID-19 epidemic shifted nearly 2 years older than
that before COVID-19 epidemic (figure 2). Prior to the COVID-19
pandemic, the age distribution during the epidemic of both viral
infections was almost similar from year to year (data not shown).
The periodic prevalence of epidemic respiratory viral infections in
children can be attributed to several factors.
First is viral evolution. Viruses have the ability to mutate and evolve
rapidly. These new strains can lead to recurrent outbreaks as the
population lacks immunity to the modified virus. Second is host
susceptibility. In a population, individuals may gain immunity to a
specific viral infection through prior exposure or vaccination. However,
over time, the immunity acquired through natural infection or
vaccination can wane. Third are changes in population density and
mobility. Population dynamics, including changes in population density
and mobility, can influence the transmission of viral infections.
Increased travel, urbanization, and global connectivity facilitate the
rapid spread of viruses across regions and continents. Fourth are
environmental factors. Certain viral infections exhibit seasonal
patterns due to environmental factors. For instance, respiratory viruses
like influenza tend to peak during the colder months when people spend
more time indoors in close proximity, providing favorable conditions for
viral transmission. Additionally, changes in climate patterns or
ecological disturbances can affect the distribution and prevalence of
vector-borne infections such as dengue or Zika virus. Fifth is lack of
universal vaccination or treatment. The absence of effective vaccines or
treatments against a particular viral infection can contribute to its
periodic prevalence.
RSV and hMPV spread through similar routes of severe acute respiratory
syndrome coronavirus 2 (SARS-CoV-2), the measures taken to control
COVID-19 have inevitably limited the transmission of both respiratory
viruses among children. Furthermore, the reduced exposure to common
respiratory viruses during the pandemic may affect the development of
natural immunity in children, potentially leading to a susceptible
population when restrictions ease and social interactions increase. One
of the reasons why children aged 3 to 4 years became more susceptible to
RSV and hMPV after the COVID-19 pandemic may be that immunity was not
stimulated due to the decrease in epidemic viral diseases during the
COVID-19 pandemic. Also, the possibility that the virus mutated during
the COVID-19 pandemic cannot be completely ruled out.
Viral interference at the individual level has been verified in animal
experiments.10,
11 However, virus interference at the
population level is observed as an indirect phenomenon and its causes
are complicated. From this perspective, a detailed examination of the
trends in infectious diseases, especially in children before and after
the rare COVID-19 pandemic will provide very important suggestions for
considering the mode of transmission of viral infections in society, the
maturation process of immunity to viruses, and countermeasures against
acute viral infection epidemics.