Epidemiological and phylogenetic characteristics of human metapneumovirus in Beijing, China, 2014-2024

In November 2024, there was an unusual surge in human metapneumovirus (hMPV) infection cases in Beijing. We performed an epidemiological investigation among cases with acute respiratory tract infection (ARTI). We enrolled ARTI cases from 35 sentinel hospitals, collected samples and medical records, conducted comprehensive pathogen testing, sequenced target genes or whole genomes, and performed phylogenetic analysis. A total of 79,793 cases were included in this study from 2014 to 2024. The hMPV epidemic exhibited typical seasonality from December to April of the following year, with an overall positivity rate of hMPV of 1.6%. The positivity rate of hMPV was highest in the 0-4 year age group (3.4%) and remained relatively high (1.2%) among populations over 60 years of age. Genotypes A and B were cocirculated, with predominant genotypes alternating every two years. We identified two variants of A2c with 180 or 111 nucleotide duplications in the G gene since 2016, and the A2c_111nt-dup has been predominant (56.9%) over the parent A2c since 2018. HMPV infection experienced an unusual surge beginning in November 2024 and peaked in December (9.5%). Subgenotype B2 (98.3%) returned to the predominant position instead of the A2c_111nt-dup and seemed to be associated with milder illness. Twenty hMPV isolates collected in 2024 were identified as known subgenotypes (A2c and B2) via whole-genome analyses. In conclusion, hMPV exhibited a typical seasonality in Beijing, with the predominant genotypes alternating every two years. Its unusual surge in November 2024 was attributed to the reoccurrence of hMPV B2 rather than a novel variant.