Multiple Influenza Virus Infections in 4 Consecutive Epidemiological Seasons: A Retrospective Study in Children and Adolescents.

Abstract

BackgroundRecent observations provide evidence for group-specific immunity toward influenza A infections and raise the question of how often we can get the flu.MethodsWe retrospectively analyzed 2308 cases of children and adolescents with clinically manifested influenza and a positive PCR-test during the last 4 epidemiological seasons (2014–15 through 2017–18).ResultsIn the 2015–16 epidemiological season, almost 12% of patients had experienced an influenza infection during the previous season; in the 2016–17 season, more than 14% had at least 1 infection during the previous 2 seasons, and in 2017–18 season, over 18% had 1 or more infections during the previous 3 seasons. The majority of these repetitive infections occurred in children between 3–8 years of age. 29 patients experienced 3 or 4 infections during these seasons, whereas 38 children had 2 influenza episodes within the same season. Epidemiological pattern of circulating viral strains changed yearly; however, we identified 5 patients with confirmed influenza B infections during the 2014–15 and 2017–18 seasons, when only subtype Yamagata was circulating in Austria.ConclusionsRepetitive influenza infections in consecutive epidemiological seasons occurred quite frequently in children and adolescents. Observations like ours contribute to a better understanding of the immunity against influenza virus infections and could have implications for future vaccination strategies.