![\"\"](\"http:\/\/www.med.niigata-u.ac.jp\/pub\/wppublichealth\/wp-content\/uploads\/2026\/01\/\u30b9\u30e9\u30a4\u30c91.jpg\")
<\/a> ![\"\"](\"http:\/\/www.med.niigata-u.ac.jp\/pub\/wppublichealth\/wp-content\/uploads\/2026\/01\/\u30b9\u30e9\u30a4\u30c92.jpg\")
<\/a> ![\"\"](\"http:\/\/www.med.niigata-u.ac.jp\/pub\/wppublichealth\/wp-content\/uploads\/2026\/01\/\u30b9\u30e9\u30a4\u30c93.jpg\")
<\/a> ![\"\"](\"http:\/\/www.med.niigata-u.ac.jp\/pub\/wppublichealth\/wp-content\/uploads\/2026\/01\/\u30b9\u30e9\u30a4\u30c94.jpg\")
<\/a><\/p>\n\u3010\u521d\u8a3a\u6642\u691c\u4f53\u3011<\/p>\n
\u521d\u8a3a\u6642\u306b\u63a1\u53d6\u3055\u308c\u305f163\u4ef6\u306e\u691c\u4f53\u306e\u5185\u8a33\u306f\u3001\u30a4\u30f3\u30d5\u30eb\u30a8\u30f3\u30b6\u30a6\u30a4\u30eb\u30b9A(H1N1)pdm09\u304c0\u4ef6\uff080%\uff09\u3001\u30a4\u30f3\u30d5\u30eb\u30a8\u30f3\u30b6\u30a6\u30a4\u30eb\u30b9A(H3N2)\u304c155\u4ef6\uff0895.1\uff05\uff09\u3001\u4e9c\u578b\u5224\u5b9a\u4e0d\u80fd\u306eA\u578b\u30a4\u30f3\u30d5\u30eb\u30a8\u30f3\u30b6\u30a6\u30a4\u30eb\u30b9\u306f2\u4ef6\uff081.2\uff05\uff09\u3001\u30a4\u30f3\u30d5\u30eb\u30a8\u30f3\u30b6\u30a6\u30a4\u30eb\u30b9B\/Victoria\u304c2\u4ef6\uff081.2%\uff09\u3001\u7cfb\u7d71\u304c\u5224\u5b9a\u3067\u304d\u306a\u304b\u3063\u305fB\u578b\u30a4\u30f3\u30d5\u30eb\u30a8\u30f3\u30b6\u304c0\u4ef6\uff080\uff05\uff09\u3067\u3057\u305f\u3002\u307e\u305f\u3001A\u578b\u304a\u3088\u3073B\u578b\u306e\u6df7\u5408\u611f\u67d3\u306f0\u4ef6\uff080.0\uff05\uff09\u3001RT-PCR\u9670\u6027\u306e\u691c\u4f53\u306f4\u4ef6\uff082.5%\uff09\u3067\u3057\u305f\uff08\u88681\uff09\u3002<\/p>\n
<\/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\u3001155\u4ef6\u306eA(H3N2)\u306e\u3046\u3061PA\/I38T\u5909\u7570\u967d\u6027\u306e\u691c\u4f53\u304c2\u691c\u4f53\u78ba\u8a8d\u3055\u308c\u307e\u3057\u305f\uff08\u691c\u51fa\u7387\uff1a1.3\uff05\uff09\uff08\u88682-1\uff09\u3002<\/p>\n
<\/p>\n
\u6b21\u4e16\u4ee3\u30b7\u30fc\u30af\u30a8\u30f3\u30b9\u89e3\u6790\u306f\u3001\u521d\u8a3a\u6642\u691c\u4f53155\u4ef6\u306e\u3046\u3061A(H3N2) 44\u4ef6\u3092\u5bfe\u8c61\u306b\u5b9f\u65bd\u3057\u307e\u3057\u305f\u3002\u305d\u306e\u7d50\u679c\u3001\u30d0\u30ed\u30ad\u30b5\u30d3\u30eb\u8010\u6027\u306b\u95a2\u9023\u3059\u308bPA\/I38T\u5909\u7570\u30921\u4ef6\u3067\u691c\u51fa\u3057\u307e\u3057\u305f\uff08\u691c\u51fa\u7387\uff1a2.3\uff05\uff09\uff08\u88682-2\uff09\u3002\u5f53\u8a72\u691c\u4f53\u306e\u30d0\u30ea\u30a2\u30f3\u30c8\u30b3\u30fc\u30eb\u89e3\u6790\u3067\u306f\u3001PA\/I38T\u5909\u7570\u306e\u5272\u5408\u304c99%\u4ee5\u4e0a\u3067\u3042\u308a\u3001\u91ce\u751f\u578b\u306f\u307b\u3068\u3093\u3069\u691c\u51fa\u3055\u308c\u305a\u3001PA\/I38T\u5909\u7570\u30a6\u30a4\u30eb\u30b9\u304c\u307b\u307c\u5168\u3066\u3092\u5360\u3081\u308b\u72b6\u614b\u3067\u3057\u305f\u3002\u306a\u304a\u3001\u3053\u306e\u75c7\u4f8b\u306f\u3001\u6cbb\u7642\u306f\u30d0\u30ed\u30ad\u30b5\u30d3\u30eb\u3067\u3057\u305f\u304c\u3001\u81e8\u5e8a\u7d4c\u904e\u306e\u8a73\u7d30\u306f\u78ba\u8a8d\u3067\u304d\u3066\u3044\u307e\u305b\u3093\u3002\u307e\u305f\u3001\u3053\u306e\u75c7\u4f8b\u306e\u518d\u8a3a\u691c\u4f53\u304c\u63a1\u53d6\u3055\u308c\u307e\u3057\u305f\u304c\u3001\u30a6\u30a4\u30eb\u30b9\u91cf\u304c\u5c11\u306a\u304f\u89e3\u6790\u3067\u304d\u307e\u305b\u3093\u3067\u3057\u305f\u3002\u30b5\u30a4\u30af\u30ea\u30f3\u30b0\u30d7\u30ed\u30fc\u30d6\u6cd5\u306b\u3088\u308b\u521d\u8a3a\u6642\u691c\u4f53\u306e\u691c\u67fb\u3067\u3001PA\/I38T\u5909\u7570\u967d\u6027\u3068\u306a\u3063\u305f\u3082\u30461\u4ef6\u306f\u672a\u3060NGS\u89e3\u6790\u3092\u884c\u3063\u3066\u3044\u307e\u305b\u3093\u3002<\/p>\n
\u307e\u305f\u3001\u521d\u8a3a\u6642\u306eA(H3N2)\u691c\u4f531\u4ef6\u3067\u3001NGS\u30d0\u30ea\u30a2\u30f3\u30c8\u30b3\u30fc\u30eb\uff08\u5909\u7570\u691c\u51fa\u95be\u50245%\uff09\u306b\u3088\u308aPA\/E23V\u304c5.7%\u691c\u51fa\u3055\u308c\u307e\u3057\u305f\u3002E23V\u306f\u8010\u6027\u95a2\u9023\u5909\u7570\u30ea\u30b9\u30c8\uff08\u4f8b\uff1aE23G\/K\/R\uff09\u306b\u542b\u307e\u308c\u305a\u6587\u732e\u5831\u544a\u3082\u78ba\u8a8d\u3067\u304d\u306a\u3044\u305f\u3081\u3001\u53c2\u8003\u6240\u898b\u3068\u3057\u3066\u8a18\u8f09\u3057\u307e\u3059\uff08\u88682\u20102\u306b\u306f\u611f\u53d7\u6027\u682a\u3068\u3057\u3066\u8a08\u4e0a\uff09\u3002<\/p>\n
<\/p>\n
\u30b5\u30f3\u30ac\u30fc\u6cd5\u306b\u3088\u308bPA\u907a\u4f1d\u5b50\u5909\u7570\u306e\u89e3\u6790\u306f\u3001\u73fe\u6642\u70b9\u3067\u306f\u672a\u5b9f\u65bd\u3067\u3059\u3002<\/p>\n
<\/p>\n
44\u4ef6\u306eA(H3N2)\u304b\u3089\u3001\u30aa\u30bb\u30eb\u30bf\u30df\u30d3\u30eb\u306b\u5bfe\u3059\u308b\u611f\u53d7\u6027\u4f4e\u4e0b\u306b\u95a2\u9023\u3059\u308bNA\u907a\u4f1d\u5b50\u5909\u7570\u306f\u3001\u6b21\u4e16\u4ee3\u30b7\u30fc\u30af\u30a8\u30f3\u30b9\u6cd5\u3067\u691c\u51fa\u3055\u308c\u307e\u305b\u3093\u3067\u3057\u305f\uff08\u88684\uff09\u3002<\/p>\n
<\/p>\n
\u3010\u518d\u8a3a\u6642\u691c\u4f53\u3011<\/p>\n
\u518d\u8a3a\u6642\u691c\u4f53\u306f86\u540d\u304b\u3089\u63a1\u53d6\u3055\u308c\u3001\u3053\u306e\u3046\u3061\u30d0\u30ed\u30ad\u30b5\u30d3\u30eb\u6cbb\u7642\u3092\u53d7\u3051\u305f\u60a3\u800548\u540d\uff08\u5168\u3066A(H3N2)\u4e9c\u578b\uff09\u306b\u3064\u3044\u3066\u3001\u6cbb\u7642\u5f8c3\uff5e7\u65e5\u76ee\u306b\u518d\u8a3a\u6642\u306e\u4e0a\u6c17\u9053\u691c\u4f53\u3092\u63d0\u4f9b\u3044\u305f\u3060\u304d\u307e\u3057\u305f\uff08\u88681\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\u6709\u7121\u3092\u8abf\u3079\u305f\u7d50\u679c\u300148\u691c\u4f53\u4e2d11\u691c\u4f53\u3067PA\/I38T\u5909\u7570\u304c\u691c\u51fa\u3055\u308c\u307e\u3057\u305f\uff08\u691c\u51fa\u7387\uff1a22.9\uff05\uff09\u3002\u3053\u306e\u3046\u30611\u691c\u4f53\u306f\u3001PA\/I38T\u5909\u7570\u306e\u3042\u308b\u30a6\u30a4\u30eb\u30b9\u306e\u307f\u304c\u691c\u51fa\u3055\u308c\u3001\u4ed610\u691c\u4f53\u306f\u5909\u7570\u306e\u306a\u3044\u30a6\u30a4\u30eb\u30b9\u3082\u540c\u6642\u306b\u691c\u51fa\u3055\u308c\u305f\u305f\u3081\u3001\u30d0\u30ed\u30ad\u30b5\u30d3\u30eb\u611f\u53d7\u6027\u682a\u3068\u8010\u6027\u5909\u7570\u682a\u304c\u6df7\u5728\u3057\u3066\u3044\u308b\u3068\u8003\u3048\u3089\u308c\u307e\u3057\u305f\u3002\u307e\u305f\u3001\u518d\u8a3a\u6642\u306bRT-PCR\u3067\u30a4\u30f3\u30d5\u30eb\u30a8\u30f3\u30b6A(H3N2)\u304c\u967d\u6027\u3067\u3042\u3063\u305f24\u691c\u4f53\u306b\u9650\u308b\u3068\u3001PA\/I38T\u5909\u7570\u306f11\u691c\u4f53\u3067\u691c\u51fa\u3055\u308c\u3001\u691c\u51fa\u5272\u5408\u306f45.8\uff05\uff0811\/24\uff09\u3067\u3057\u305f\uff08\u88682-1\uff09\u3002\u3053\u308c\u3089\u306e11\u4f8b\u306e\u3046\u3061\u30014\u4f8b\u306e\u75c7\u72b6\u306e\u7d4c\u904e\u304c\u78ba\u8a8d\u3067\u304d\u3066\u304a\u308a\u3001\u6709\u71b1\u6642\u9593\u306f\u305d\u308c\u305e\u308c\u30010\u6642\u9593\u30017\u6642\u9593\u3001105\u6642\u9593\u3001133\u6642\u9593\u3067\u3057\u305f\u3002\u4ed6\u306e\u60a3\u8005\u306e\u6709\u71b1\u6642\u9593\u3084\u6709\u75c7\u72b6\u671f\u9593\u306e\u8a73\u7d30\u306f\u78ba\u8a8d\u4e2d\u3067\u3059\u3002<\/p>\n
\u307e\u305f\u30011\u75c7\u4f8b\u306b\u3064\u3044\u3066\u306f\u518d\u8a3a\u306e1\u65e5\u5f8c\u306b\u3082\u3046\u4e00\u56de\u691c\u4f53\u304c\u63a1\u53d6\u3055\u308c\u3066\u304a\u308a\uff08\u518d\u3005\u8a3a\uff09\u3001\u518d\u8a3a\u691c\u4f53\u3067\u306f\u30d0\u30ed\u30ad\u30b5\u30d3\u30eb\u611f\u53d7\u6027\u682a\u3068\u8010\u6027\u5909\u7570\u682a\u304c\u6df7\u5728\u3057\u3066\u3044\u307e\u3057\u305f\u304c\u3001\u518d\u3005\u8a3a\u691c\u4f53\u3067\u306f\u3001PA\/I38T\u306e\u8010\u6027\u5909\u7570\u682a\u306e\u307f\u304c\u691c\u51fa\u3055\u308c\u307e\u3057\u305f\u3002<\/p>\n
<\/p>\n
86\u4ef6\u306e\u518d\u8a3a\u6642\u691c\u4f53\u306e\u3046\u3061\u3001NGS\u691c\u67fb\u3092\u5b9f\u65bd\u3057\u305f\u306e\u306f8\u4ef6\u3067\u3001\u305d\u306e\u3046\u30617\u4ef6\u304c\u30d0\u30ed\u30ad\u30b5\u30d3\u30eb\u6295\u4e0e\u5f8c\u30011\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\u3053\u306e\u30d0\u30ed\u30ad\u30b5\u30d3\u30eb\u6295\u4e0e\u5f8c\u306e7\u691c\u4f53\uff08\u5168\u3066A(H3N2)\uff09\u306eNGS\u89e3\u6790\u3067\u306f\u30014\u4ef6\u3067\u30c7\u30fc\u30bf\u89e3\u6790\u304c\u53ef\u80fd\u3067\u3001PA\u907a\u4f1d\u5b50\u306e\u5909\u7570\u306f4\u4ef6\u4e2d2\u4ef6\u3067\u78ba\u8a8d\u3055\u308c\u307e\u3057\u305f\u3002\u691c\u51fa\u3055\u308c\u305f\u5909\u7570\u306f\u3044\u305a\u308c\u3082PA\/I38T\u3067\u3001\u30d0\u30ea\u30a2\u30f3\u30c8\u30b3\u30fc\u30eb\u983b\u5ea6\u306f\u305d\u308c\u305e\u308c20.8\uff05\u300154.7\uff05\u3067\u3057\u305f\u3002PA\u5909\u7570\u306e\u691c\u51fa\u7387\u306f\u89e3\u6790\u5bfe\u8c617\u4ef6\u3092\u5206\u6bcd\u3068\u3059\u308b\u306828.6\uff05\uff082\/7\uff09\u3001\u89e3\u6790\u304c\u6210\u529f\u3057\u305f4\u4ef6\u3092\u5206\u6bcd\u3068\u3059\u308b\u306850.0\uff05\uff082\/4\uff09\u3067\u3057\u305f\u3002<\/p>\n
<\/p>\n
\u30aa\u30bb\u30eb\u30bf\u30df\u30d3\u30eb\u6295\u4e0e\u5f8c\u306e\u518d\u8a3a\u6642\u306b\u63a1\u53d6\u3055\u308c\u305fA(H3N2)\u691c\u4f531\u4ef6\u306b\u3064\u3044\u3066NGS\u89e3\u6790\u3092\u5b9f\u65bd\u3057\u307e\u3057\u305f\u304c\u3001\u89e3\u6790\u306b\u5fc5\u8981\u306a\u30c7\u30fc\u30bf\u304c\u5f97\u3089\u308c\u307e\u305b\u3093\u3067\u3057\u305f\u3002<\/p>\n
<\/p>\n
<\/p>\n
Overview of Influenza Circulating Strains and Antiviral Drug-Resistant Strains in Japan During the 2025-2026 Season (<\/strong>As of January 15, 2026<\/strong>)<\/strong><\/p>\n Between October 2025 and January 15, 2026, 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 <\/p>\n Participating Medical Institutions and Sample Collection<\/strong><\/p>\n Outpatient medical institutions in eight 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 <\/p>\n Baseline (pre-treatment) specimens<\/strong><\/p>\n Among 163 baseline specimens, influenza A(H1N1)pdm09 was detected in 0 specimens (0%), influenza A(H3N2) in 155 specimens (95.1%), unsubtyped influenza A in 2 specimens (1.2%), influenza B\/Victoria in 2 specimens (1.2%), and influenza B with undetermined lineage in 0 specimens (0%). No mixed A and B infections were identified (0.0%), and 4 specimens (2.5%) were RT-PCR negative (Table 1).<\/p>\n \u00a0<\/strong><\/p>\n For baseline pre-treatment influenza A specimens, we screened for the PA\/I38T substitution using the cycling-probe RT-PCR method. PA\/I38T-positive specimens were identified in 2 of 155 A(H3N2) specimens (detection rate: 1.3%) (Table 2-1).<\/p>\n <\/p>\n NGS analysis was performed for 44 of the 155 baseline A(H3N2) specimens. As a result, the PA\/I38T substitution associated with reduced susceptibility to baloxavir was detected in 1 specimen (detection rate: 2.3%) (Table 2-2). Variant-calling analysis showed that the PA\/I38T variant frequency was \u226599%, indicating that wild-type virus was barely detectable and that the PA\/I38T variant population accounted for almost the entire viral population in the specimen. For this case, baloxavir was used for treatment; however, detailed clinical course information could not be confirmed. A follow-up specimen was collected from this case, but the viral load was low and sequencing analysis was not successful. For the other baseline specimen that was PA\/I38T-positive by the cycling-probe method, NGS analysis has not yet been performed.<\/p>\n <\/p>\n In addition, in one baseline A(H3N2) specimen, PA\/E23V was detected at 5.7% by NGS variant calling (variant detection threshold: 5%). Because E23V is not included in the list of baloxavir resistance-associated substitutions by WHO (e.g., E23G\/K\/R) and no published reports have been identified, this finding is described as a reference (this sample is counted as a susceptible virus in Table 2-2).<\/p>\n <\/p>\n Sanger sequencing for PA gene substitutions has not been performed to date.<\/p>\n <\/p>\n Among the 44 baseline A(H3N2) specimens analyzed by NGS, no NA gene substitutions associated with reduced susceptibility to oseltamivir were detected (Table 4).<\/p>\n <\/p>\n <\/p>\n Follow-up (post-treatment) specimens<\/strong><\/p>\n Follow-up (post-treatment) specimens were collected from 86 patients. Among them, 48 patients, all A(H3N2), had a follow up sample collection 3\u20137 days after the start of baloxavir treatment (Table 1).<\/p>\n <\/p>\n Using the cycling-probe RT-PCR method, PA\/I38T was detected in 11 of the 48 follow-up specimens (detection rate: 22.9%). In one specimen, only the PA\/I38T variant virus was detected, whereas in the remaining 10 specimens, wild-type virus was also detected, suggesting mixed populations of baloxavir-susceptible virus and resistance-associated variants. When analysis was restricted to the 24 follow-up specimens that were RT-PCR positive for influenza A(H3N2), PA\/I38T was detected in 11 specimens, corresponding to a detection proportion of 45.8% (11\/24) (Table 2-1). Among these 11 cases, symptom courses were available for 4 cases, with fever duration of 0 hours, 7 hours, 105 hours, and 133 hours, respectively. Detailed information on fever duration and symptom duration for the remaining patients is under confirmation.<\/p>\n <\/p>\n In one case, an additional specimen (a second follow-up visit) was collected one day after the follow-up visit. While the first follow-up specimen contained a mixed population of baloxavir-susceptible virus and PA\/I38T variant virus, only the PA\/I38T variant virus was detected in the second follow-up specimen.<\/p>\n <\/p>\n Among the 86 follow-up specimens, NGS was performed for 8 specimens: 7 specimens collected after baloxavir treatment and 1 specimen collected after oseltamivir treatment (Tables 2-2 and 4). For the 7 post-baloxavir A(H3N2) specimens, sequencing analysis was successful in 4 specimens, and PA gene substitutions were identified in 2 of these 4 specimens. The detected substitutions were PA\/I38T in both specimens, with variant frequencies of 20.8% and 54.7%, respectively. The detection rate of PA substitutions was 28.6% (2\/7) when calculated using all 7 specimens as the denominator, and 50.0% (2\/4) when calculated using the 4 specimens with successful analysis as the denominator.<\/p>\n <\/p>\n For the single follow-up A(H3N2) specimen collected after oseltamivir treatment, NGS was performed; however, no sufficient data for analysis were obtained.<\/p>\n","protected":false},"excerpt":{"rendered":"