Influenza and Influenza-Like Virus Infection in Children Under 14 Years of Age: An Investigation of 725 Cases in the 2021/2022 Influenza Epidemic Season in Poland.

BACKGROUND Influenza in children poses a significant health problem worldwide. In this study we investigated 725 cases of influenza and influenza-like virus infection in children under 14 years of age in the 2021/2022 influenza epidemic season in Poland. MATERIAL AND METHODS The material for the study (nose and throat swabs) was collected during the 2021/2022 epidemic season. We analyzed 725 samples from the National Influenza Center, Department of Influenza Research at the National Institute of Public Health NIH-NRI or at 16 Voivodship Sanitary Epidemiological Stations across Poland. Quantitative polymerase chain reaction (qRT-PCR) was applied to determine the influenza virus type and subtype (in RNA isolated from positive samples). RESULTS This study shows the high incidence of influenza among children under the age of 14. Most confirmed infections were caused by influenza A. The genetic material of the A/H1N1/pdm09 subtype was not found among the analyzed samples. The highest number of influenza A infections was among the youngest children (the 0-4 years age group). The most common influenza-like virus was respiratory syncytial virus (RSV). The greatest number of cases caused by this respiratory virus was registered among the youngest children (0-4 years). CONCLUSIONS This study, which shows the high incidence of influenza among children under the age of 14, highlights the importance of regular influenza vaccination. Since children often play a dominant role in spreading influenza virus in the community, regular vaccination can have both health and economic benefits for all age groups.