Overview of seasonal influenza and recommended vaccine during the 2016/2017 season in Nepal

Background: Influenza is a highly contagious viral respiratory infection caused by influenza viruses whose epidemic and pandemic have resulted in significant morbidity and mortality. The annual epidemic of influenza results in an estimated 3-5 million cases of severe illness and about 290000-650000 deaths globally. The vaccination program has been successful to control the epidemic however, it further needs improvement. This study was aimed to investigate the types of influenza viruses prevailing in Nepal during 2016 and, to match the recommended vaccine for use during the same season. Methods: A descriptive cross sectional study was carried out at National Public Health Laboratory, Kathmandu, Nepal for the period of one year (Jan-Dec 2016). A total of 1683 throat swab specimen was collected from patients of different age group referred to NPHL for influenza testing. The specimen was primarily stored at 4 degrees C and processed using ABI 7500 RT PCR system for the identification of influenza viruses. Results: Of the total 1683 patients suspected of having influenza infection, influenza viruses were isolated from 614 (36.5%) patients with male predominance. The highest number of infection was caused by influenza A/H3 strain (51.0%) followed by influenza B (40.4%) and influenza A (H1N1) pdm09 (8.6%). Two peaks of infection were observed during the year 2016. The widely available trivalent vaccine during the season did not match the prevailing strain because of the dominance of B/Yamagata lineage over B/Victoria lineage. Conclusion: We concluded that Nepal experiences semiannual cycle of influenza infection, firstly during the month of January-February and secondly during the month of July-August. The vaccine to be introduced in Nepal need to be decided by national authority based on prevailing influenza types to confer effective immunization.