Incident changes in the prevalence of respiratory virus among children during COVID-19 pandemic in Hangzhou, China.

Dear editor,

The report entitled "Nonpharmaceutical interventions reduced the incidence and exacerbation of allergic diseases in children during the COVID-19 pandemic" by Ye et al. aroused our strong concern. In a report, Ye et al. announced that the incidence of allergic diseases in children during the COVID-19 epidemic was reduced and that the exacerbation of diseases in allergic patients was also reduced. Here, we presented the prevalence of the respiratory virus among children during the COVID-19 pandemic in Hangzhou, China.

Adenoviruses (Ads) are nonenveloped icosahedral viruses with a diameter of ∼ 90 nm and slight structural differences between genotypes. More than 80% of diagnosed adenovirus infections occur in children under four years old (due to lack of humoral immunity). Adenovirus infections may occur in healthy children or adults in closed or crowded environments (particularly military recruits). ,

Respiratory syncytial virus (RSV) was discovered more than 50 years ago. It has since been identified as the most common cause of acute respiratory tract infections in infants.4, 5, 6 Influenza viruses are members of the Orthomyxoviridae family. There are seven genera: Alpha influenza virus (influenza A virus), Beta influenza virus (influenza B virus), Gamma influenza virus (influenza C virus), Delta influenza virus (influenza D virus), Isa virus, Quaranja virus and Thogoto virus. Influenza A and B viruses often cocirculate annually during seasonal epidemics and can cause severe respiratory diseases in humans. The clinical course of both influenza A and B virus infections can vary from mild symptoms in some cases to a severe respiratory infection characterized by clinical complications that lead to hospitalization and death in some cases.

Infection with these respiratory viruses has a certain seasonality. According to clinical observations, during the COVID-19 pandemic in Hangzhou, there was a significant difference in the number of children with respiratory infections.

The Health Commission of Zhejiang Province released confirmed cases of COVID-19 in Zhejiang Province on January 23, 2020. From the end of 2020 to the beginning of 2021, vaccinations against SARS-CoV-2 for all age groups were launched one after another. In this study, we analyzed children who came to the outpatient clinic of Children's Hospital of Zhejiang University School of Medicine from January 2019 to October 2021, analyzed the number of positive people for the above four respiratory viruses (Fig. 1 ), and calculated the positive detection rate (number of positive detections of a certain virus/number of visits in the same period) (Fig. 2 ). Therefore, in this study, we compared the number of respiratory virus infections and positive infection rates in children during the year before the COVID-19 pandemic, the first year after the outbreak, and the second year after the outbreak (mass vaccination) to explore the prevalence of the respiratory virus in the COVID-19 pandemic.

Fig. 1

The number of positive detections of various respiratory viruses at different times (years).

Fig. 2

The positive detection rate of various viruses at different times (years).

According to the data results, in 2020, there were the fewest outpatient visits and the fewest positive infections in the three years, followed by 2021. The number of visits in 2019 was the largest. In 2019, adenoviruses, influenza A and influenza B had apparent seasonality, while their seasonality was not fully highlighted in 2020 and 2021. The number of infections and infection rates was highest in 2019, followed by 2021, and the lowest in 2020. The number in 2021 is higher than that in 2020, which may be related to the short-term relaxation of protection awareness after universal vaccination. The respiratory syncytial virus showed a rebound increase in 2021 (higher than 2019). Data for 2021 show that people's awareness of protection may decrease slightly after vaccination, resulting in more infections than in 2020. On the other hand, wearing a mask for a long time may increase children's susceptibility to respiratory viruses, which requires further research.

To simplify, the COVID-19 pandemic has changed the prevalence of respiratory viruses among children in Hangzhou. This change may not be due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) itself but mainly due to a series of strict measures taken during the COVID-19 pandemic. First, strict control measures, such as wearing masks and prohibiting large-scale gatherings, have cut off the transmission of respiratory viruses to a certain extent. At the same time, improving people's awareness of protection and the importance of physical fitness has also reduced the infection of respiratory viruses. China has adopted a "dynamic zero" policy against SARS-CoV-2. The spread of SARS-CoV-2 in China is currently under control, but the global pandemic continues, and new variants of SARS-CoV-2 have emerged. , Therefore, the prevalence of respiratory viruses in children is still uncertain and deserves our attention and continuous monitoring. It should be noted that the limitations of this study are as follows: as a single-center study, conclusions in other regions may be different. The specific measures controlling the infection of respiratory viruses should be further researched in multiple centers.

In short, during the COVID-19 pandemic, nonpharmacological interventions reduced the infection rate of children's respiratory viruses. Continuous testing helps prevent a major outbreak of respiratory virus infection in the later stages of the epidemic.

Declaration of Competing Interest

All authors have declared that there are no conflicts of interest.