![\"\"](\"http:\/\/www.med.niigata-u.ac.jp\/pub\/wppublichealth\/wp-content\/uploads\/2026\/03\/\u30b9\u30e9\u30a4\u30c91.jpg\")
<\/a><\/p>\n\u30a4\u30f3\u30d5\u30eb\u30a8\u30f3\u30b6\u30a6\u30a4\u30eb\u30b9\u306f2024\u5e7411\u6708\u4e0b\u65ec\uff08\u7b2c48\u9031\uff09\u304b\u3089\u691c\u4f53\u6570\u304c\u5897\u52a0\u3057\u300112\u6708\u4e0b\u65ec\u304b\u30891\u6708\u4e0a\u65ec\u306b\u304b\u3051\u3066\u30d4\u30fc\u30af\u306b\u9054\u3057\u307e\u3057\u305f\u3002\u6d41\u884c\u5f53\u521d\u304b\u3089A(H1N1)pdm09\u304c\u591a\u304f\u691c\u51fa\u3055\u308c\u30012024-25\u30b7\u30fc\u30ba\u30f3\u306e\u6d41\u884c\u306e\u30d4\u30fc\u30af\u306f\u3001A(H1N1)pdm09\u306b\u3088\u308b\u3082\u306e\u3068\u63a8\u5b9a\u3055\u308c\u307e\u3059\u3002\u305d\u306e\u5f8c\u3001\u60a3\u8005\u6570\u306f\u5f90\u3005\u306b\u6e1b\u5c11\u3057\u3001\u672c\u5dde\u3067\u306f2025\u5e744\u6708\u9803\uff08\u7b2c17\u9031\uff09\u307e\u3067\u6d41\u884c\u304c\u7d9a\u304d\u307e\u3057\u305f\u3002\u4ee5\u524d\u306f\u30011\u6708\u304b\u30892\u6708\u306b\u6d41\u884c\u306e\u30d4\u30fc\u30af\u304c\u307f\u3089\u308c\u307e\u3057\u305f\u304c\u3001\u65b0\u578b\u30b3\u30ed\u30ca\u611f\u67d3\u75c7\u30d1\u30f3\u30c7\u30df\u30c3\u30af\u4ee5\u964d\u3001\u6d41\u884c\u6642\u671f\u304c\u65e9\u307e\u3063\u3066\u304a\u308a\u30012024-25\u30b7\u30fc\u30ba\u30f3\u306f\u5e74\u672b\u306b\u6d41\u884c\u306e\u30d4\u30fc\u30af\u304c\u78ba\u8a8d\u3055\u308c\u307e\u3057\u305f\u3002\u5e74\u672b\u5e74\u59cb\u306e\u4f11\u8a3a\u671f\u9593\u3068\u6d41\u884c\u62e1\u5927\u304c\u91cd\u306a\u3063\u305f\u3053\u3068\u304c\u3001\u7279\u5fb4\u7684\u306a\u75ab\u5b66\u7684\u6240\u898b\u3068\u8003\u3048\u3089\u308c\u307e\u3059\u3002\u305d\u306e\u5f8c\u3001A(H3N2)\u3084B\u578b\uff08B\/Victoria\u7cfb\u7d71\uff09\u304c\u5c11\u6570\u691c\u51fa\u3055\u308c\u307e\u3057\u305f\u304c\u3001\u5c0f\u898f\u6a21\u306a\u6d41\u884c\u306b\u3068\u3069\u307e\u308a\u307e\u3057\u305f\u30022025\u5e745\u6708\u4ee5\u964d\u306e\u30a4\u30f3\u30d5\u30eb\u30a8\u30f3\u30b6\u30a6\u30a4\u30eb\u30b9\u306e\u691c\u51fa\u306f\u3001\u4e3b\u306b\u6c96\u7e04\u306b\u304a\u3051\u308bA(H3N2)\u306e\u7d99\u7d9a\u7684\u306a\u691c\u51fa\u306b\u3088\u308b\u3082\u306e\u3067\u3001\u8abf\u67fb\u671f\u9593\u304c\u7d42\u4e86\u3059\u308b9\u6708\u4e0b\u65ec\u307e\u3067\u5c11\u6570\u306a\u304c\u3089\u6bce\u6708\u60a3\u8005\u304c\u78ba\u8a8d\u3055\u308c\u307e\u3057\u305f\u3002<\/p>\n
<\/p>\n
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<\/p>\n \u6cbb\u7642\u524d\u306b\u63a1\u53d6\u3055\u308c\u305f\u30a4\u30f3\u30d5\u30eb\u30a8\u30f3\u30b6A\u578b\u306e\u691c\u4f53\u306b\u3064\u3044\u3066\u3001\u30b5\u30a4\u30af\u30ea\u30f3\u30b0\u30d7\u30ed\u30fc\u30d6RT-PCR\u6cd5\u306b\u3088\u308aPA\/I38T\u5909\u7570\u306e\u691c\u51fa\u3092\u8a66\u307f\u305f\u7d50\u679c\u300169\u4ef6\u306eA(H1N1)pdm09\u306841\u4ef6\u306eA(H3N2)\u304b\u3089\u3001PA\/I38T\u5909\u7570\u967d\u6027\u306e\u691c\u4f53\u306f\u78ba\u8a8d\u3055\u308c\u307e\u305b\u3093\u3067\u3057\u305f\uff08\u691c\u51fa\u7387\uff1a\uff10\uff05\uff09\uff08\u88682-1\uff09\u3002<\/p>\n <\/p>\n \u6b21\u4e16\u4ee3\u30b7\u30fc\u30af\u30a8\u30f3\u30b9\uff08NGS\uff09\u89e3\u6790\u306b\u3088\u308bPA\u5909\u7570\u306e\u691c\u51fa\u89e3\u6790\u3067\u306f\u3001\u521d\u8a3a\u6642\u691c\u4f5383\u4ef6\u306e\u3046\u3061A(H1N1)pdm09 57\u4ef6\u3001A(H3N2) 22\u4ef6\u3001B\/Victoria 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\u3010\u518d\u8a3a\u6642\u691c\u4f53\u3011<\/p>\n \u518d\u8a3a\u6642\u691c\u4f53\u306f13\u540d\u304b\u3089\u63a1\u53d6\u3055\u308c\u30019\u4ef6\u304c\u30d0\u30ed\u30ad\u30b5\u30d3\u30eb\u6295\u4e0e\u5f8c\u30014\u4ef6\u304c\u30aa\u30bb\u30eb\u30bf\u30df\u30d3\u30eb\u6295\u4e0e\u5f8c\u306e\u691c\u4f53\u3067\u3057\u305f\uff08\u88682-2\u3001\u88684\uff09\u3002<\/p>\n <\/p>\n \u3053\u308c\u3089\u306e\u691c\u4f53\u306b\u5bfe\u3057\u3066\u3001\u30b5\u30a4\u30af\u30ea\u30f3\u30b0\u30d7\u30ed\u30fc\u30d6RT-PCR\u6cd5\u3092\u7528\u3044\u3066PA\/I38T\u5909\u7570\u306e\u691c\u51fa\u3092\u8a66\u307f\u305f\u7d50\u679c\u3001PA\/I38T\u5909\u7570\u967d\u6027\u306e\u691c\u4f53\u306f\u78ba\u8a8d\u3055\u308c\u307e\u305b\u3093\u3067\u3057\u305f\uff08\u691c\u51fa\u7387\uff1a\uff10\uff05\uff09\uff08\u88682-1\uff09\u3002<\/p>\n <\/p>\n 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Type\u3068\u306eMix\uff09\u304c\u78ba\u8a8d\u3055\u308c\u307e\u3057\u305f\uff08\u88683\uff09\u3002\u691c\u51fa\u7387\u306f\u5168\u4f53\uff085\u4ef6\uff09\u306720.0\uff05\u3001\u89e3\u6790\u53ef\u80fd\u691c\u4f53\uff084\u4ef6\uff09\u3067\u306f25.0%\u3067\u3057\u305f\u3002\u30b5\u30f3\u30ac\u30fc\u6cd5\u306b\u3088\u308a\u5909\u7570\u304c\u691c\u51fa\u3055\u308c\u305f\u691c\u4f53\u306f\u3001NGS\u306b\u3088\u308b\u89e3\u6790\u306e\u7d50\u679c\u3067\u306f\u3001\u5909\u7570\u306f\u78ba\u8a8d\u3055\u308c\u307e\u305b\u3093\u3067\u3057\u305f\u3002\u306a\u304a\u3001\u5909\u7570\u3042\u308a\u306e\u5224\u5b9a\u306f\u3001NGS\u53ca\u3073\u30b5\u30f3\u30ac\u30fc\u6cd5\u306e\u4e21\u65b9\u3067\u5909\u7570\u304c\u78ba\u8a8d\u3055\u308c\u305f\u5834\u5408\u3068\u3057\u3066\u304a\u308a\u3001\u30b5\u30f3\u30ac\u30fc\u6cd5\u306b\u3088\u308aPA\u5909\u7570\u304c\u691c\u51fa\u3055\u308c\u305f\u3053\u306e\u691c\u4f53\u306f\u3001NGS\u306b\u3088\u308b\u89e3\u6790\u3067\u306f\u3001\u5909\u7570\u306f\u78ba\u8a8d\u3055\u308c\u307e\u305b\u3093\u3067\u3057\u305f\u306e\u3067\u3001\u5909\u7570\u306a\u3057\u3068\u7dcf\u5408\u5224\u5b9a\u3057\u3066\u3044\u307e\u3059\u3002<\/p>\n <\/p>\n \u30aa\u30bb\u30eb\u30bf\u30df\u30d3\u30eb\u6295\u4e0e\u5f8c\u306e\u518d\u8a3a\u6642\u306b\u63a1\u53d6\u3055\u308c\u305f4\u4ef6\uff08\u3059\u3079\u3066A(H1N1)pdm09\uff09\u306b\u5bfe\u3057NGS\u89e3\u6790\u3092\u5b9f\u65bd\u3057\u3001\u3046\u30613\u4ef6\u3067\u30c7\u30fc\u30bf\u89e3\u6790\u304c\u53ef\u80fd\u3067\u3057\u305f\uff08\u88684\uff09\u3002\u305d\u306e\u3046\u30612\u4ef6\u304b\u3089NA\u907a\u4f1d\u5b50\u306e\u5909\u7570\u304c\u691c\u51fa\u3055\u308c\u3001\u691c\u51fa\u7387\u306f\u5168\u4f53\uff084\u4ef6\uff09\u306750.0\uff05\u3001\u89e3\u6790\u53ef\u80fd\u691c\u4f53\uff083\u4ef6\uff09\u3067\u306f66.6\uff05\u3067\u3057\u305f\u3002\u691c\u51fa\u3055\u308c\u305f\u5909\u7570\u306f\u3001\u521d\u8a3a\u6642\u306bNA\/S247N\u5909\u7570\u304c\u78ba\u8a8d\u3055\u308c\u3066\u3044\u305f\u60a3\u8005\u306e\u518d\u8a3a\u6642\u691c\u4f53\u3067\u540c\u5909\u7570\u304c\u7d99\u7d9a\u3057\u3066\u691c\u51fa\u3055\u308c\u305f\u3082\u306e\uff08\u30d0\u30ea\u30a2\u30f3\u30c8\u30b3\u30fc\u30eb\uff1a99.6\uff05\uff09\u3068\u3001\u65b0\u305f\u306bNA\/N295S\u5909\u7570\u304c\u78ba\u8a8d\u3055\u308c\u305f1\u4ef6\uff08\u30d0\u30ea\u30a2\u30f3\u30c8\u30b3\u30fc\u30eb\uff1a18.7\uff05\uff09\u3067\u3057\u305f\u3002<\/p>\n <\/p>\n Overview of Influenza Circulating Strains and Antiviral Drug-Resistant Strains in Japan During the 2024-25 Season (As of March 6, 2026)<\/strong><\/p>\n Between October 2024 and September 2024, we conducted a study in Japan to monitor circulating influenza strains and the emergence of antiviral resistance. The study focused on detecting substitutions in the PA gene associated with reduced susceptibility to baloxavir and substitutions in the NA gene associated with reduced susceptibility to neuraminidase inhibitors, including oseltamivir.<\/p>\n \u00a0<\/strong><\/p>\n Participating Medical Institutions and Sample Collection<\/strong><\/p>\n Outpatient medical institutions in seven prefectures participated in this study. Upper respiratory tract samples were collected as initial samples from patients who visited these institutions with suspected influenza symptoms (influenza-like illness, ILI), such as fever, cough, sore throat, and fatigue. These patients were confirmed positive for influenza A or B using rapid diagnostic tests (RDTs). For patients treated with baloxavir, upper respiratory tract samples were also collected during follow-up visits 3\u20137 days after treatment. All clinical specimens were sent to Niigata University, where real-time RT-PCR was performed for influenza virus detection, type\/subtype determination, detection of the PA\/I38T substitution (for A(H1N1)pdm09 and A(H3N2)), and detection of the NA\/H275Y substitution (for A(H1N1)pdm09). Next-generation sequencing (NGS) and Sanger sequencing were used to confirm PA and NA substitutions.<\/p>\n \u00a0<\/strong><\/p>\n Influenza Epidemic Curve<\/strong><\/p>\n The number of influenza virus-positive patients was aggregated weekly based on sample collection dates to construct an epidemic curve (Figure 1). Influenza viruses were detected from late November 2024 (week 48), and the number of specimens increased thereafter, reaching a peak from late December to early January. A(H1N1)pdm09 was frequently detected from the early phase of the epidemic, suggesting that the peak of the 2024\u201325 season was mainly attributable to A(H1N1)pdm09. Thereafter, the number of patients gradually decreased, and in Honshu, influenza circulation persisted until approximately April 2025 (week 17).Before the COVID-19 pandemic, the seasonal peak typically occurred between January and February; however, since the pandemic, the timing of influenza epidemics has shifted earlier, and in the 2024\u201325 season the peak was observed at the end of the year. The overlap between the year-end and New Year holiday clinic closures and the expansion of the epidemic is considered a characteristic epidemiological finding. Subsequently, A(H3N2) and type B viruses (B\/Victoria lineage) were detected in small numbers, but these remained limited to small-scale outbreaks. After May 2025, influenza virus detections were mainly due to the continued detection of A(H3N2) in Okinawa, and sporadic cases were observed monthly until the study concluded in late September.<\/p>\n \u00a0<\/strong><\/p>\n Baseline (pre-treatment) specimens<\/strong><\/p>\n Among 128 baseline specimens collected at the initial visit, influenza A(H1N1)pdm09 was detected in 69 specimens (53.9%), influenza A(H3N2) in 41 specimens (32.0%), unsubtyped influenza A in 0 specimens (0%), influenza B\/Victoria in 11 specimens (8.6%), and influenza B with undetermined lineage in 3 specimens (2.3%). No mixed A and B infections were identified (0.0%), and 4 specimens (3.1%) were RT-PCR negative (Table 1).<\/p>\n <\/p>\n For baseline pre-treatment influenza A specimens, we screened for the PA\/I38T substitution using the cycling-probe RT-PCR method. No PA\/I38T-positive specimens were identified among the 69 A(H1N1)pdm09 and 41 A(H3N2) specimens (detection rate: 0%) (Table 2-1).<\/p>\n <\/p>\n NGS analysis for PA substitutions was performed for 83 baseline specimens, including 57 A(H1N1)pdm09, 22 A(H3N2), and 4 B\/Victoria specimens. As a result, no substitutions associated with reduced susceptibility to baloxavir were detected (detection rate: 0%) (Table 2-2).<\/p>\n <\/p>\n Sanger sequencing analysis of PA gene substitutions was performed for 62 A(H1N1)pdm09, 18 A(H3N2), and 14 influenza B specimens (including B\/Victoria and influenza B with undetermined lineage). As a result, no substitutions associated with reduced susceptibility to baloxavir were detected (detection rate: 0%) (Table 3).<\/p>\n <\/p>\n NGS analysis for NA substitutions was also performed for 83 baseline specimens, including 57 A(H1N1)pdm09, 22 A(H3N2), and 4 B\/Victoria specimens. As a result, four oseltamivir resistance\u2013associated substitutions were detected in A(H1N1)pdm09 specimens: one NA\/S247N substitution and three NA\/H275Y substitutions (detection rate: 7.0%) (Table 4). Variant-calling analysis showed that the frequencies of these substitutions were all \u226599%, indicating that the variant viruses were predominant in these specimens. No resistance-associated substitutions were detected in A(H3N2) or B\/Victoria specimens (detection rate: 0%).<\/p>\n \u00a0<\/strong><\/p>\n Follow-up (post-treatment) specimens<\/strong><\/p>\n Follow-up (post-treatment) specimens were collected from 13 patients. Among them, 9 specimens were collected after baloxavir treatment and 4 specimens after oseltamivir treatment (Tables 2-2 and 4).<\/p>\n <\/p>\n Using the cycling-probe RT-PCR method, we screened for the PA\/I38T substitution in these specimens. As a result, no PA\/I38T-positive specimens were identified (detection rate: 0%) (Table 2-1).<\/p>\n <\/p>\n NGS analysis was performed for the 9 follow-up specimens collected after baloxavir treatment (all A(H1N1)pdm09). Sequencing analysis was successful in 1 specimen, and no substitutions associated with reduced susceptibility to baloxavir were detected (detection rate: 0%) (Table 2-2). The remaining 8 specimens could not be analyzed by NGS.<\/p>\n <\/p>\n Sanger sequencing analysis of PA gene substitutions was performed for 5 A(H1N1)pdm09 specimens. As a result, an I38I\/F PA amino acid substitution (mixed with wild-type virus) was identified in one A(H1N1)pdm09 strain (Table 3). The detection rate was 20.0% when calculated using all 5 specimens as the denominator and 25.0% when calculated using the 4 specimens for which sequence analysis was successful. The specimen in which the substitution was detected by Sanger sequencing did not show any substitution in the NGS analysis. In this study, a substitution was considered present only when confirmed by both NGS and Sanger sequencing. Therefore, this specimen was determined as having no substitution.<\/p>\n <\/p>\n NGS analysis was performed for the 4 follow-up specimens collected after oseltamivir treatment (all A(H1N1)pdm09), and sequencing analysis was successful in 3 specimens (Table 4). NA gene substitutions were detected in 2 of these specimens. The detection rate was 50.0% when calculated using all 4 specimens as the denominator and 66.6% when calculated using the 3 specimens with successful sequence analysis as the denominator. The detected substitutions consisted of continued detection of the NA\/S247N substitution (variant call frequency: 99.6%) in the follow-up specimen from a patient in whom this substitution had already been identified at the initial visit, and one newly detected NA\/N295S substitution (variant call frequency: 18.7%).<\/p>\n","protected":false},"excerpt":{"rendered":"<\/a> <\/a> <\/a> <\/a> <\/a><\/p>\n