Characterization of influenza A(H3N2) strains circulating in Argentina during the 2017 season

Background: Influenza A viruses are an important cause of severe infectious diseases in humans and are characterized by their fast evolution rate. The continuous antigenic drift of these virus significantly contributes to the emergence of new strains and the reduced effectiveness of the vaccine. In 2017, influenza A(H3N2) (FLUA/H3) was the predominant circulating virus detected, followed by both influenza B virus lineages in very low proportion. This year, the FLUA/H3 vaccine component in Argentina was A/Hong Hong/4801/2014 and belonged to clade 3C.2a. Recent publications have shown evidence for suboptimal vaccine effectiveness against laboratory-confirmed FLUA/H3 infection due to the circulation of variants capable of causing disease even in vaccinated patients. Here, we report the diversity of FLUA/H3 viruses circulating in Argentina and try to estimate their temporality across the 2017 season. Methods & Materials: The Argentine National Influenza Center (NIC) routinely receives influenza positive respiratory specimens collected from pediatric and adult inpatients and outpatients coming from all the country for isolation and further characterization. Between January and October, the NIC received a total of 2,663 influenza positive samples and 1,952 viruses were characterized as FLUA/H3. A set of 44 viruses collected between EW 13-30 was selected for sequencing the HA1 of the HA (986 bp). Sequences were analyzed using BioEdit and MEGA 6 programs. Results: Sequencing analysis shown the detection of one clade 3C.2a related to the vaccine virus and one subclade 3C.2a1 related to a new FLUA/H3 virus that emerged in the last Northern Hemisphere season called A/Bolzano/7/2016. The dominant virus subcluster was 3C.2a/T31K/R142K (54.5%) related with the vaccine H3 component followed by 3C.2a1/N171K/T135K (18.2%), and 3C.2a1/N171K/N121K / K92R/H311Q (13,6%), both related with the new virus Bolzano. In the early season (EW13-19), 70% of the circulating viruses were related to recently emerged viruses, however, in the middle and latter season (EW 20-30) the 69.7% of the viruses were related to vaccine H3 component. Conclusion: The genetic analysis of the Argentinean FLUA/H3 viruses demonstrated a co-circulation of viruses from vaccine clade 3C.2a and Bolzano subclade 3C.2a1 and a temporal distribution of these variants through the season.