CDC maintains low public health risk despite more cases, the first reported death, and accelerated vaccine development to enhance pandemic preparedness.
Interactive CDC case map
Image credits: CDC
As of April 2025, the CDC has reported 70 confirmed and probable human cases of H5N1 avian influenza since the outbreak began in 2024 in the United States. The majority of these cases have been linked to exposure through commercial agricultural settings, with 41 individuals exposed through infected dairy herds and 24 associated with poultry farms and culling operations. Two additional cases were connected to other animal exposures, including backyard flocks and wild birds, and three remain of unknown origin. Most human cases have been mild. Although, one fatality has been recorded in Louisiania this past January, marking the first H5N1-related death in the US.
This Louisiana case was the first severe human infection with H5N1 reported in the country and was identified as the D11 genotype, a strain previously associated with more serious illness. This includes a critical case in a Canadian child who required ECMO but ultimately recovered. In contrast, the B313 genotype, which has caused most cases among farm workers in the US has been linked to only mild symptoms. Investigations found no evidence of additional infections or person-to-person transmission, and this remains the only reported case in Louisiana.
Since late February 2024, more than 179,000 specimens have been tested through the national influenza surveillance system, which has detected six H5 cases. Targeted surveillance focusing on individuals with direct animal exposure has monitored more than 16,400 people and tested over 880; this led to the identification of 64 cases two months ago.
The H5N1 outbreak began in dairy cows in March 2024 and has significantly impacted animal populations. As of mid-April 2025, the virus has been detected in more than 12,700 wild birds across 51 jurisdictions, affected over 167 million poultry, and spread to 1,009 dairy herds in 17 states. Despite the virus’s widespread presence in animals, the CDC reports no signs of unusual influenza activity in people and emphasizes that the risk to the general public remains low.
The United States has reported 70 human H5N1 cases, including one death, with no evidence of person-to-person transmission.
The virus has spread widely among birds and dairy herds, prompting extensive national surveillance and testing efforts.
The FDA has fast-tracked ARCT-2304, a self-amplifying mRNA vaccine now in Phase 1 trials, as part of pandemic preparedness efforts.
In response to the ongoing threat, the FDA granted Fast Track designation on April 10 to ARCT-2304, Arcturus Therapeutics’ investigational self-amplifying mRNA vaccine for protection against H5N1 avian influenza. Also known as LUNAR-H5N1, the vaccine is designed for rapid and scalable deployment during a pandemic and is part of the company’s proprietary STARR mRNA platform. The Fast Track status will accelerate development and regulatory review, enabling more frequent communication with the FDA and potential eligibility for Priority Review.
ARCT-2304 entered Phase 1 clinical trials in November 2024, enrolling 200 healthy adults across the US to evaluate different dosing strategies and immune responses. Interim results are expected in the second half of 2025. The self-amplifying mRNA technology enables in vivo mRNA amplification, meaning smaller doses can still generate strong immune responses. This provides a significant advantage over conventional mRNA and egg-based vaccines. Additionally, the vaccine is lyophilized and refrigerator-stable, simplifying distribution and storage.
