Monitoring the sensitivity of influenza viruses to oseltamivir, in Romania, from 2016 to 2023

Introduction: influenza is an acute viral disease caused by infection of the upper respiratory tract - difficult to control, which affects a large part of the population. Neuraminidase inhibitors (NAIs), such as oseltamivir and zanamivir, are the antiviral drugs utilized in Romania for the treatment of respiratory infections caused by the influenza viruses. The objective of the study is to monitor and analyze influenza viruses circulating in Romania, in terms of their susceptibility to oseltamivir, with the aim of signalling the emergence of viral strains resistant to antivirals. Methods: The phenotypic method was performed to evaluate the inhibitory effect of oseltamivir on the neuraminidase enzyme activity of influenza viruses. Genotypic methods (SNP-based assays or sequencing of neuraminidase/whole genome) were used for detecting amino acid substitutions associated with influenza antiviral resistance. The study period is from 2016 to 2023. Results: from the total number of influenza viruses isolated during the period (833 isolated), 670 strains were characterized antigenically and genetically, and the phenotypic susceptibility to antivirals was performed for 245 isolated viral strains. According to WHO criteria categories antiviral susceptibility based on IC50 data, none of the test results indicated reduced or highly reduced inhibition by oseltamivir. Conclusion: This monitoring, carried out in the National Influenza Center Romania - Cantacuzino NMMIRD, is extremely important to maintain effective flu control and further development of other antiviral agents.