Parechovirus-A3 Infection in Neonates and Young Infants from the Pre-Coronavirus Disease 2019 Pandemic Period to the Post-Restriction Era from the Pediatric Parechovirus Surveillance Group in Japan

BACKGROUND: The coronavirus disease 2019 (COVID-19) pandemic affected the epidemiology of community-acquired infectious diseases; however, the data on the effects of the pandemic on parechovirus-A3 (PeV-A3) circulation remain incomplete. METHODS: This prospective multicenter observational study was conducted by the Pediatric Parechovirus Surveillance Group in Japan, comprising 12 prefectures, from 2019 to 2023. Febrile neonates and infants younger than 4 months, who were suspected of having sepsis, meningitis, and/or encephalitis and required hospitalization, were included. Parechovirus-A (PeV-A) was detected in the serum and/or cerebrospinal fluid samples by real-time PCR and genotyped by direct sequencing. A phylogenetic tree was constructed based on the viral protein 1 region. RESULTS: Overall, 131 patients were diagnosed with PeV-A infections. Before the pandemic in 2019, 36 patients (27.5%) were reported. Early in the pandemic, the number declined: seven (5.3%) in 2020, one (0.8%) in 2021, and 27 (20.6%) in 2022; however, the number increased to 60 (45.8%) after the removal of restrictions in 2023. Genotype analyses demonstrated that 124 (94.7%) patients had PeV-A3. The median age of PeV-A3 infected patients and peak months (July-August) were similar between 2019 and 2023. PeV-A3 evolved into a single clade and divided into two branches. CONCLUSIONS: The number of neonates and young infants infected with PeV-A, mostly PeV-A3, significantly decreased at the beginning of the COVID-19 pandemic; however, the number increased in 2023. Our national surveillance system helped demonstrate the situations in PeV-A3-infected patients from the pre-pandemic period to the post-restriction era in Japan.