Human parainfluenza viruses (HPIVs) are the leading causes of acute respiratory tract infections (ARTIs), particularly in children. During the COVID-19 pandemic, non-pharmaceutical interventions (NPIs) significantly influenced the epidemiology of respiratory viruses. This study analyzed 19,339 respiratory specimens from pediatric patients with ARTIs to detect HPIVs using PCR or tNGS, focusing on the period from 2021 to 2023. HPIVs were identified in 1395 patients (7.21%, 1395/19,339), with annual detection rates of 6.86% (303/4419) in 2021, 6.38% (331/5188) in 2022, and 7.82% (761/9732) in 2023. Notably, both the total number of tests and HPIV-positive cases increased in 2023 compared to 2021 and 2022. Seasonal analysis revealed a shift in HPIV prevalence from winter and spring in 2021–2022 to spring and summer in 2023. Most HPIV-positive cases were in children aged 0–7 years, with fewer infections among those aged 7–18 years. Since June 2022, HPIV-3 has been the most prevalent serotype (59.55%, 524/880), whereas HPIV-2 had the lowest proportion (0.80%, 7/880). The proportions of HPIV-1 (24.89%, 219/880) and HPIV-4 (15.45%, 136/880) were similar. Additionally, the incidence of co-infections with other common respiratory pathogens has increased since 2021. This study highlights rising HPIV detection rates post-COVID-19 and underscores the need for continuous surveillance of HPIVs to inform public health strategies for future epidemic seasons.

Human adenoviruses (HAdVs) are significant viral pathogens associated with a wide spectrum of diseases, particularly acute respiratory tract infections (ARTIs) in children. This study aimed to characterize the epidemiological features of HAdV infections among hospitalized pediatric patients in Hainan Province, China, from January 2021 to December 2024, encompassing the COVID-19 pandemic and post-policy transition period. Among 31,843 hospitalized children with ARTIs, HAdVs were detected in 2464 cases (7.74%). Annual positivity rates were 4.87% in 2021, 7.21% in 2022, and 4.39% in 2023, and sharply increased to 11.58% in 2024. No significant sex-based difference in infection rates was observed. Distinctly seasonal and temporal patterns were noted, with a pronounced summer peak in 2024 and increased circulation throughout the year. A notable shift in dominant genotypes was observed, with HAdV-C initially prevailing, followed by a surge in HAdV-B between late 2023 and mid-2024. Children aged 1–7 years exhibited the highest positivity rates, indicating age-related susceptibility. Furthermore, co-infections were common and became increasingly predominant after the implementation of tNGS diagnostics, accounting for over 85% of HAdV-positive cases by 2023–2024. These findings suggest a post-pandemic resurgence of HAdV activity, shaped by altered population immunity, resumed social contact, and improved diagnostic sensitivity. Continuous molecular and epidemiological surveillance is essential to guide targeted interventions and inform pediatric respiratory infection management strategies.