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![\"\"](\"http:\/\/www.med.niigata-u.ac.jp\/pub\/wppublichealth\/wp-content\/uploads\/2025\/05\/DRAFT_2024-25-Report_20250519\u78ba\u8a8d\u7528-.jpg\")
<\/a>\n\u30b5\u30a4\u30af\u30ea\u30f3\u30b0\u30d7\u30ed\u30fc\u30d6RT-PCR\u6cd5\u3092\u7528\u3044\u3066\u3001\u6cbb\u7642\u524d\u306b\u63a1\u53d6\u3055\u308c\u305f\u30a4\u30f3\u30d5\u30eb\u30a8\u30f3\u30b6A\u578b\u306e\u691c\u4f53\u304b\u3089\u3001PA\/I38T\u5909\u7570\u306e\u691c\u51fa\u3092\u8a66\u307f\u305f\u7d50\u679c\u300155\u4ef6\u306eA(H1N1)pdm09\u306814\u4ef6\u306eA(H3N2)\u306e\u3044\u305a\u308c\u304b\u3089\u3082PA\/I38T\u5909\u7570\u306f\u78ba\u8a8d\u3055\u308c\u307e\u305b\u3093\u3067\u3057\u305f\uff08\u691c\u51fa\u7387\uff1a0\uff05\uff09\uff08\u88682-1\uff09\u3002
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![\"\"](\"http:\/\/www.med.niigata-u.ac.jp\/pub\/wppublichealth\/wp-content\/uploads\/2025\/05\/DRAFT_2024-25-Report_20250519\u78ba\u8a8d\u75282-.jpg\")
<\/a><\/p>\n\u30d0\u30ed\u30ad\u30b5\u30d3\u30eb\u6cbb\u7642\u3092\u53d7\u3051\u305f\u60a3\u8005\u306e\u3046\u30612\u540d\uff08A(H1N1)pdm09\u304c2\u540d\u3001A(H3N2)\u306f0\u540d\uff09\u306f\u3001\u6cbb\u7642\u5f8c3\uff5e7\u65e5\u76ee\u306b\u518d\u8a3a\u3057\u305f\u969b\u3001\u4e0a\u6c17\u9053\u691c\u4f53\u3092\u63d0\u4f9b\u3044\u305f\u3060\u304f\u3053\u3068\u304c\u3067\u304d\u307e\u3057\u305f\u3002\u518d\u8a3a\u6642\u306b\u63a1\u53d6\u3055\u308c\u305f\u691c\u4f53\u306b\u3064\u3044\u3066\u3001\u30b5\u30a4\u30af\u30ea\u30f3\u30b0\u30d7\u30ed\u30fc\u30d6RT-PCR\u6cd5\u3092\u7528\u3044\u3066PA\/I38T\u5909\u7570\u3092\u8abf\u3079\u305f\u7d50\u679c\u3001\u3044\u305a\u308c\u306e\u691c\u4f53\u304b\u3089\u3082PA\/I38T\u5909\u7570\u306f\u691c\u51fa\u3055\u308c\u307e\u305b\u3093\u3067\u3057\u305f\uff08\u691c\u51fa\u7387\uff1a0\uff05\uff09\u3002\u691c\u67fb\u7d50\u679c\u306e\u5185\u8a33\u306f\u30011\u4ef6\u304cPA\/I38T\u5909\u7570\u7121\u3057\uff08\u611f\u53d7\u6027\u682a\uff09\u30011\u4ef6\u304cPCR\u9670\u6027\u3067\u3057\u305f\uff08\u88682-1\uff09\u3002<\/p>\n
\u6b21\u4e16\u4ee3\u30b7\u30fc\u30b1\u30f3\u30b5\u30fc\uff08NGS\uff09\u306b\u3088\u308b\u5168\u30b2\u30ce\u30e0\u89e3\u6790\u3092\u7528\u3044\u3066\u3001PA\u907a\u4f1d\u5b50\u304a\u3088\u3073NA\u907a\u4f1d\u5b50\u306b\u3064\u3044\u3066\u3001\u611f\u53d7\u6027\u4f4e\u4e0b\u3092\u793a\u3059\u5909\u7570\u3092\u8abf\u67fb\u3057\u307e\u3057\u305f\u3002 \u3010PA\u907a\u4f1d\u5b50\u89e3\u6790\u3011 \u3010NA\u907a\u4f1d\u5b50\u89e3\u6790\u3011 \u3010HA\u907a\u4f1d\u5b50\u306b\u3088\u308b\u7cfb\u7d71\u6a39\u89e3\u6790\u3011 Participating Medical Institutions and Sample Collection Summary of Initial Sample Results Detection of PA\/I38T Substitution in Pre-Treatment Samples Follow-Up Samples After Baloxavir Treatment Whole-Genome Analysis Using Next-Generation Sequencing (NGS) PA Gene Analysis Pending Analyses NA Gene Analysis Phylogenetic Tree Analysis of HA gene
\nNGS\u3067\u89e3\u6790\u3067\u304d\u305f\u521d\u8a3a\u6642\u691c\u4f53\u306f\u300117\u4ef6\u3067\u3057\u305f\u3002\u305d\u306e\u5185\u8a33\u306f\u3001\u30a4\u30f3\u30d5\u30eb\u30a8\u30f3\u30b6\u30a6\u30a4\u30eb\u30b9A(H1N1)pdm09\u304c12\u4ef6\u3001\u30a4\u30f3\u30d5\u30eb\u30a8\u30f3\u30b6\u30a6\u30a4\u30eb\u30b9A(H3N2)\u304c3\u4ef6\u3001\u30a4\u30f3\u30d5\u30eb\u30a8\u30f3\u30b6\u30a6\u30a4\u30eb\u30b9B\/Victoria\u304c2\u4ef6\u3067\u3059\uff08\u88682-2\u3001\u88684\uff09\u3002
\n<\/a>
\n<\/a><\/p>\n
\n\u521d\u8a3a\u6642\u306b\u63a1\u53d6\u3055\u308c\u305f\u691c\u4f53\u306b\u304a\u3044\u3066\u3001\u30d0\u30ed\u30ad\u30b5\u30d3\u30eb\u306b\u5bfe\u3059\u308b\u611f\u53d7\u6027\u4f4e\u4e0b\u3092\u793a\u3059\u3068\u5831\u544a\u3055\u308c\u305f\u5909\u7570\u306f\u78ba\u8a8d\u3055\u308c\u307e\u305b\u3093\u3067\u3057\u305f\uff08\u88682-2\uff09\u3002
\n\u30d0\u30ed\u30ad\u30b5\u30d3\u30eb\u6295\u4e0e\u5f8c\u306e\u518d\u8a3a\u6642\u306b\u63a1\u53d6\u3055\u308c\u305f\u691c\u4f53\u306e\u3046\u3061\u3001A(H1N1)pdm09\u306f1\u4ef6\u3001A(H3N2)\u306f0\u4ef6\u3001B\/Victoria\u306f0\u4ef6\u3001NGS\u306b\u3088\u308a\u89e3\u6790\u3059\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3057\u305f\u3002
\n\u3044\u305a\u308c\u306e\u691c\u4f53\u304b\u3089\u3082\u30d0\u30ed\u30ad\u30b5\u30d3\u30eb\u306b\u5bfe\u3059\u308b\u611f\u53d7\u6027\u4f4e\u4e0b\u3092\u793a\u3059\u3068\u5831\u544a\u3055\u308c\u305f\u5909\u7570\u306f\u78ba\u8a8d\u3055\u308c\u307e\u305b\u3093\u3067\u3057\u305f\u3002\uff08\u691c\u51fa\u7387\uff1a0\uff05\uff09\u3002
\n\u306a\u304a\u3001\u30b5\u30f3\u30ac\u30fc\u6cd5\u3092\u7528\u3044\u305fPA\u907a\u4f1d\u5b50\u306e\u5909\u7570\u691c\u51fa\u306f\u3001\u73fe\u6642\u70b9\u3067\u306f\u307e\u3060\u5b9f\u65bd\u3055\u308c\u3066\u3044\u307e\u305b\u3093\u3002<\/p>\n
\n\u521d\u8a3a\u6642\u306b\u63a1\u53d6\u3055\u308c\u305f\u691c\u4f53\u306e\u3046\u3061\u3001\u30aa\u30bb\u30eb\u30bf\u30df\u30d3\u30eb\u306b\u5bfe\u3059\u308b\u611f\u53d7\u6027\u4f4e\u4e0b\u3092\u793a\u3059\u3068\u5831\u544a\u3055\u308c\u3066\u3044\u308bNA\/S247N\u5909\u7570\u304c\u3001A(H1N1)pdm09\u30671\u4ef6\u691c\u51fa\u3055\u308c\u307e\u3057\u305f\uff08\u691c\u51fa\u7387\uff1a8.3\uff05\uff09\uff08\u88684\uff09\u3002\u30d0\u30ea\u30a2\u30f3\u30c8\u30b3\u30fc\u30eb\uff08\u5909\u7570\u5272\u5408\u89e3\u6790\uff09\u306e\u7d50\u679c\u3001\u3053\u306e\u691c\u4f53\u4e2d\u306b\u5909\u7570\u30a6\u30a4\u30eb\u30b9\u304c\u5360\u3081\u308b\u5272\u5408\u306f99.6%\u3067\u3057\u305f\u3002\u305d\u306e\u4ed6\u306e\u691c\u4f53\u306b\u304a\u3044\u3066\u3001\u30aa\u30bb\u30eb\u30bf\u30df\u30d3\u30eb\u306b\u5bfe\u3059\u308b\u611f\u53d7\u6027\u4f4e\u4e0b\u3092\u793a\u3059\u3068\u5831\u544a\u3055\u308c\u305f\u5909\u7570\u306f\u78ba\u8a8d\u3055\u308c\u307e\u305b\u3093\u3067\u3057\u305f\u3002
\n\u30aa\u30bb\u30eb\u30bf\u30df\u30d3\u30eb\u6295\u4e0e\u5f8c\u306e\u518d\u8a3a\u6642\u306b\u63a1\u53d6\u3055\u308c\u305f\u691c\u4f53\u306e\u3046\u3061\u3001NGS\u306b\u3088\u308a\u89e3\u6790\u3067\u304d\u305f\u3082\u306e\u306f\u3001A(H1N1)pdm09\u304c3\u4ef6\u3001A(H3N2)\u304a\u3088\u3073B Victoria\u306f\u305d\u308c\u305e\u308c0\u4ef6\u3067\u3057\u305f\u3002
\n\u518d\u8a3a\u6642\u306b\u63a1\u53d6\u3055\u308c\u305f\u691c\u4f53\u306e\u3046\u3061\u3001A(H1N1)pdm09\u306b\u304a\u3044\u3066\u30012\u3064\u306eNA\u5909\u7570\u304c\u691c\u51fa\u3055\u308c\u307e\u3057\u305f\uff08\u691c\u51fa\u7387\uff1a66.6\uff05\uff09\u3002NA\/N295S\u5909\u7570\u304c1\u4ef6\u3001\u521d\u8a3a\u6642\u306bNA\/S247N\u5909\u7570\u304c\u78ba\u8a8d\u3055\u308c\u305f\u60a3\u8005\u306e\u518d\u8a3a\u6642\u691c\u4f53\u3067NA\/S247N\u5909\u7570\u304c1\u4ef6\u691c\u51fa\u3055\u308c\u307e\u3057\u305f\u3002\u30d0\u30ea\u30a2\u30f3\u30c8\u30b3\u30fc\u30eb\u306e\u7d50\u679c\u3001NA\/N295S\u5909\u7570\u306f18.7\uff05\u3001NA\/S247N\u5909\u7570\u306f99.6\uff05\u3067\u3057\u305f\u3002<\/p>\n
\n2024\u5e7410\u6708\u4ee5\u964d\u306b\u65e5\u672c\u3067\u691c\u51fa\u3055\u308c\u305f\u30a4\u30f3\u30d5\u30eb\u30a8\u30f3\u30b6A(H1N1)pdm09\u306e\u30d8\u30de\u30b0\u30eb\u30c1\u30cb\u30f3\u907a\u4f1d\u5b50\uff08HA\uff09\u306e\u6a39\u5f62\u56f3\u89e3\u6790\u3092\u5b9f\u65bd\u3044\u305f\u3057\u307e\u3057\u305f\uff08\u56f3\uff11\uff09\u3002
\n\u4eca\u56de\u89e3\u6790\u3057\u305f\u691c\u4f53\u306f\u3059\u3079\u30665a.2a\uff08C.1.9.3\uff09\u7cfb\u7d71\u306b\u5206\u985e\u3055\u308c\u3066\u304a\u308a\uff08\u8d64\u4e38\uff09\u3001\u73fe\u5728\u4e16\u754c\u7684\u306b\u6d41\u884c\u3057\u3066\u3044\u308b\u682a\u3068\u4e00\u81f4\u3057\u3066\u3044\u308b\u3053\u3068\u304c\u78ba\u8a8d\u3055\u308c\u307e\u3057\u305f\u3002
\n\u306a\u304a\u30012024-2025\u5e74\u30b7\u30fc\u30ba\u30f3\u306e\u30ef\u30af\u30c1\u30f3\u682a\uff08A\/Victoria(\u30d3\u30af\u30c8\u30ea\u30a2) \/4897\/2022(IVR-238)\uff09\u306b\u8a72\u5f53\u3059\u308b5a.2a.1\u682a\u306f\u3001\u73fe\u6642\u70b9\u3067\u306f\u65e5\u672c\u3067\u306f\u307e\u3060\u691c\u51fa\u3055\u308c\u3066\u304a\u308a\u307e\u305b\u3093\u3002
\nOverview of Influenza Circulating Strains and Antiviral Drug-Resistant Strains in Japan During the 2024-2025 Season (As of May 14, 2025)
\nBetween October 2024 and May 14, 2025, we conducted a study across Japan to monitor influenza activity and the emergence of influenza virus strains with drug-resistant substitutions. This study aimed to detect substitutions in the PA gene, which reduce sensitivity to baloxavir, and substitutions in the NA gene, which reduce sensitivity to neuraminidase inhibitors, including oseltamivir.<\/p>\n
\nOutpatient 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 for influenza virus detection, subtype determination, and PA and NA substitution detection using real-time PCR(RT-PCR), Sanger sequencing, and next-generation sequencing (NGS).<\/p>\n
\nAmong the 78 samples collected during the initial visit, 55 samples (70.5%) were identified as influenza A(H1N1)pdm09, while 14 samples (17.9%) were identified as influenza A(H3N2). No cases of unsubtypeable influenza A virus were detected (0.0%). Influenza B\/Victoria was detected in eight samples (10.3%). There were no cases of mixed A and B infections (0.0%). Additionally, one sample (1.3%) tested negative by RT-PCR (Table 1).<\/p>\n
\nCycling probe RT-PCR was used to detect the PA\/I38T substitution in pre-treatment influenza A samples. The substitution was not detected in any of the 55 A(H1N1)pdm09 or the 14 A(H3N2) samples analyzed, resulting in a detection rate of 0% (Table 2-1).<\/p>\n
\nAmong the patients treated with baloxavir, two individuals, both of whom had A(H1N1)pdm09, returned for follow-up 3\u20137 days after treatment and provided upper respiratory tract samples. Cycling probe RT-PCR analysis revealed that neither of these samples carried the PA\/I38T substitution, yielding a detection rate of 0%. Among the two samples, one was classified as a susceptible strain without the PA\/I38T substitution, while the other tested negative by PCR (Table 2-1).<\/p>\n
\nWe conducted whole-genome analysis using NGS to investigate substitutions associated with reduced drug sensitivity in the PA and NA genes.
\nA total of 17 initial samples were successfully analyzed by NGS. Among these, twelve samples were identified as A(H1N1)pdm09, three sample was A(H3N2), and two sample was B\/Victoria (Tables 2-2 and 4).<\/p>\n
\nIn the initial samples, no substitutions previously reported to be associated with reduced sensitivity to baloxavir were detected (Table 2-2).
\nAmong the follow-up samples collected after baloxavir treatment, NGS analysis was successfully conducted on one A(H1N1)pdm09 sample, while no A(H3N2) or B\/Victoria samples were available for analysis. No substitutions associated with reduced sensitivity to baloxavir were detected in any of these samples, resulting in a detection rate of 0%.<\/p>\n
\nAs of now, substitution detection in the PA gene using Sanger sequencing has not yet been conducted.<\/p>\n
\nAmong the initial samples, the NA\/S247N substitution, which has been reported to confer reduced sensitivity to oseltamivir, was detected in one A(H1N1)pdm09 sample, corresponding to a detection rate of 8.3% (Table 4). Variant calling analysis revealed that the proportion of substituted viruses within this sample was 99.6%. No other substitutions associated with reduced sensitivity to oseltamivir were detected in any of the other samples.
\nAmong the follow-up samples collected after oseltamivir treatment, NGS analysis was successfully conducted on three A(H1N1)pdm09 samples, while no A(H3N2) or B\/Victoria samples were available for analysis. Among these follow-up samples, the substitutions confer reduced susceptibility to oseltamivir were found in two samples(66.6%). One was NA\/N295S substitution, and another one was NA\/S247N substitution detected from the follow-up sample of a patient with confirmed NA\/S247N substitution at the initial visit. Variant calling analysis revealed that the proportion of substituted viruses within this sample was 18.7% in NA\/N295S positive sample and 99.6% in NA\/S247N sample.<\/p>\n
\nA phylogenetic tree analysis of the hemagglutinin (HA) gene of influenza A(H1N1)pdm09 detected in Japan since October 2024 was conducted (Figure 1). All the samples analyzed in this study belonged to the 5a.2a (C.1.9.3) lineage, which was confirmed to be consistent with strains currently circulating globally. The 5a.2a.1 strain, which is included in the 2024-2025 vaccine\uff08vaccine strain : A\/Victoria \/4897\/2022(IVR-238)\uff09, has not yet been detected in Japan as of now.<\/p>\n","protected":false},"excerpt":{"rendered":"