Changing landscape of pediatric influenza in Northern Mexico: A comparative clinical and virological study

Influenza remains a significant health burden in children, yet its clinical behavior and viral dynamics have shifted in recent years. These changes are particularly relevant in regions where multiple respiratory viruses co-circulate and surveillance resources are limited.

To examine how the clinical and virological profile of pediatric influenza has evolved in northern Mexico, by comparing two well-defined seasonal periods, and to contextualize these findings within national surveillance trends.

An observational, cross-sectional study was conducted in a pediatric referral hospital, including children hospitalized with acute respiratory infections during two influenza seasons (2018-2019 and 2023-2024). Clinical characteristics, laboratory findings, and RT-qPCR results were analyzed, and national surveillance reports were reviewed to identify parallel trends.

A total of 274 patients were included (137 per period). Compared to the 2018-2019 cohort, the 2023-2024 cohort demonstrated a significant reduction in influenza positivity (16.8 % vs. 5.1 %, p < 0.001) and no influenza-related deaths; however, hospitalizations were more prolonged, and inflammatory markers were higher. At the national level, ILI/SARI reports increased (from 62,729 to 180,532), and confirmed influenza cases rose (from 7632 to 13,679), while positivity (from 12.2 % to 7.6 %) and mortality (from 828 to 456) declined.

In this pediatric hospital cohort, post-pandemic seasons showed fewer influenza cases and deaths but greater clinical severity, suggesting altered host responses after reduced viral exposure. National trends indicated broader detection of respiratory cases alongside lower influenza positivity, consistent with strengthened surveillance and evolving viral circulation in Mexico.