J Korean Med Sci.  2022 Aug;37(34):e258. 10.3346/jkms.2022.37.e258.

Respiratory Syncytial Virus Outbreak Without Influenza in the Second Year of the Coronavirus Disease 2019 Pandemic: A National Sentinel Surveillance in Korea, 2021–2022 Season

• Kim JH
• Kim HY
• Lee M
• Ahn JG
• Baek JY
• Kim MY
• Huh K
• Jung J
• Kang JM

• KMID: 2532754
• DOI: http://doi.org/10.3346/jkms.2022.37.e258

Abstract

Background
This study aimed to investigate whether respiratory syncytial virus (RSV) and influenza virus (IFV) infections would occur in 2021–2022 as domestic nonpharmaceutical interventions (NPIs) are easing.
Methods
Data were collected from the Korean Influenza and Respiratory Virus Monitoring System database. The weekly positivity rates of respiratory viruses and number of hospitalizations for acute respiratory infections were evaluated (January 2016–2022). The period from February 2020 to January 2022 was considered the NPI period. The autoregressive integrated moving average model and Poisson analysis were used for data analysis. Data from 14 countries/regions that reported positivity rates of RSV and IFV were also investigated.
Results
Compared with the pre-NPI period, the positivity and hospitalization rates for IFV infection during 2021–2022 significantly decreased to 0.0% and 1.0%, respectively, at 0.0% and 1.2% of the predicted values, respectively. The RSV infection positivity rate in 2021–2022 was 1.8-fold higher than that in the pre-NPI period at 1.5-fold the predicted value. The hospitalization rate for RSV was 20.0% of that in the pre-NPI period at 17.6% of the predicted value. The re-emergence of RSV and IFV infections during 2020–2021 was observed in 13 and 4 countries, respectively.
Conclusion
During 2021–2022, endemic transmission of the RSV, but not IFV, was observed in Korea.

Keyword

Respiratory Syncytial Virus; Influenza; Nonpharmaceutical Intervention; COVID-19; South Korea

Figure

• 

  Fig. 1 Trend of COVID-19 and individual mobility in South Korea. (A) Daily number of confirmed cases of COVID-19, (B, C) monthly individual movement estimation through mobile phones, (D) respiratory syncytial virus-positivity rate in the specimen-based surveillance, and (E) influenza virus-positivity rate in the specimen-based surveillance, January 2020–January 2022.COVID-19 = coronavirus disease 2019, RSV = respiratory syncytial virus, IFV = influenza virus.The baseline was the median value, for the corresponding day of the week, during the 5-week period from January 3, 2020, to February 6, 2020.

• 

  Fig. 2 Weekly respiratory syncytial virus and influenza virus trends from Korean influenza and respiratory virus monitoring system, January 2016–January 2022. The solid lines denote the observed or predicted value. Light blue color denotes 95% confidence intervals of the predicted value and the dark blue, 80% confidence intervals of the predicted value. (A) RSV-positivity rates in the specimen-based surveillance, (B) RSV-related hospitalization cases in the clinical surveillance, (C) IFV-positivity rates in the specimen-based surveillance, and (D) IFV-related hospitalization cases in the clinical surveillance.RSV = respiratory syncytial virus, IFV = influenza virus.

• 

  Fig. 3 Heatmap of positivity rates in the national sentinel surveillance of 14 countries/regions. (A) Respiratory syncytial virus and (B) influenza virus.RSV = respiratory syncytial virus, IFV = influenza virus.Gray indicates absence of data: some countries did not operate surveillance systems during non-epidemic periods.

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