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{Excerpts} Recent updates Laboratory CDC completed serology testing on blood specimens from close contacts of a child with mild illness in San Francisco who was confirmed to be positive for avian influenza A(H5N1) virus, though, there were no known animal exposures associated with that case.  -- Serology testing was conducted to look for antibodies to influenza A(H5N1) virus in this child, which would indicate recent infection.  -- The child's blood was tested and found to have antibodies to avian influenza A(H5N1) virus.  -- None of the close contacts of the case in San Francisco who were tested had antibodies to avian influenza A(H5N1) virus, which supports the conclusion that none of these close contacts were infected , and that no person-to-person spread occurred among these close contacts.  -- These findings are reassuring. To date, human-to-human transmission of influenza A(H5) virus has not been identified in the United States. CDC has sequenced the virus from...

Summary Background More than 115 000 cases of mpox have been confirmed since the onset of a global outbreak in 2022. In addition to global transmission of clade II monkeypox virus (MPXV), the recent spread of clade I has caused a Public Health Emergency of International Concern . The third-generation smallpox vaccine modified vaccinia Ankara–Bavarian Nordic (MVA-BN) was recommended for at-risk populations in 2022, despite a scarcity of data on safety and effectiveness against mpox. Methods We did a prospective, multicentre, observational study, enrolling men who have sex with men and transgender people aged 18 years or older with changing sexual partners in Germany (Safety and Effectiveness of MVA-BN Vaccination Against MPXV Infection [SEMVAc]) between July 7, 2022, and Dec 31, 2023, evaluating safety and reactogenicity of one and two doses of subcutaneous MVA-BN. Vaccine effectiveness was estimated using risk ratios from the Kaplan–Meier estimator in an emulated retrospective target t...

Summary Background The United States Department of Agriculture has recently released reports that show samples collected from 2022 to 2025 of highly pathogenic avian influenza (H5N1) have been detected in mammals and birds . Up to February 2025, the United States Centres for Disease Control and Prevention reports that there have been 67 humans infected with H5N1 since 2024 with 1 death. The broader potential impact on human health remains unclear. Methods In this study, we computationally model 1804 protein complexes consisting of various H5 isolates from 1959 to 2024 against 11 haemagglutinin domain 1 (HA1)- neutralising antibodies . This was performed using AI-based protein folding and physics-based simulations of the antibody-antigen interactions. We analysed binding affinity changes over time and across various antibodies using multiple biochemical and biophysical binding metrics. Findings This study shows a trend of weakening binding affinity of existing antibodies against H5 isol...

Abstract High pathogenicity (HP) avian influenza viruses (AIV) generally evolve from low pathogenicity (LP) precursors after transmission from wild birds to chickens (Gallus gallus domesticus) and turkeys (Meleagris gallopavo), causing severe economic losses worldwide. Turkeys are more susceptible to AIV infection than chickens and are considered potential bridging hosts that facilitate the emergence of HPAIV . Beyond the polybasic cleavage site (pCS) in hemagglutinin (HA), little is known about other virulence determinants of HPAIV in these species. In 2015, HPAIV H7N7 and its LP ancestor were isolated from the same chicken farm, which differed by 16 nonsynonymous mutations across all eight gene segments, in addition to the pCS. Here we identify the genetic determinants, including the pCS, that contributed to the HPAIV H7N7 virulence, transmission, replication, and tissue distribution in chickens and turkeys. Notably, the non-structural (NS1) or matrix (M) proteins ’ encoding segments...