Molecular epidemiology of human metapneumovirus before and after COVID-19 in East Japan in 2017–2022

Human metapneumovirus (hMPV) is genetically classified into two major subgroups, A and B, based on attachment glycoprotein (G) gene sequences, and the A2 subgroup is further separated into three subdivisions A2a, A2b (A2b1), and A2c (A2b2). The appearance of subgroup A2c viruses carrying a 180- or 111-nucleotide duplication in the G gene (A2c_180nt-dup or A2c_111nt-dup) have been reported in Japan and Spain. The pandemic of coronavirus disease 2019 (COVID-19) disrupted the epidemiological kinetics of other respiratory viruses, including hMPV. In this study, we analysed the sequences of hMPV isolates obtained from 2017 to 2022 in Tokyo and Fukushima, i.e., before and after COVID-19. Subgroup A hMPVs were detected in 2017 to 2019, and most cases were A2c_111nt-dup, suggesting there was continuous momentum of this clade, identical to the global situation. Subgroup B, but not subgroup A, viruses were detected in 2022, after the COVID-19 peak. Phylogenetic analysis showed that these resumed subgroup B viruses were closely related to the viruses detected in 2013 to 2016 in Yokohama and in 2019 in Fukushima, suggesting a reappearance of local endemic viruses in East Japan.