Avian Influenza Targeting Dairy Cow Mammary Tissue Suppressed 1,000-Fold by mRNA Vaccination
Background
Highly Pathogenic Avian Influenza (HPAI) clade 2.3.4.4b H5N1 virus, which has begun spreading primarily among US dairy farms, is following a path distinct from traditional poultry-centric infection patterns. Instead of the respiratory system, the virus primarily replicates in the mammary tissue of dairy cows, causing severe mastitis and a sharp decline in milk production. Transmission between farms is also occurring through the milking process and viral shedding in milk.
Existing avian influenza response systems have relied mainly on poultry culling or inactivated vaccines. Traditional inactivated vaccines take months to produce and are designed to focus on systemic respiratory immunity, showing limitations in blocking the virus in bovine mammary epithelial cells and local secretory systems. To rapidly control the surging infection rates in livestock and reduce the risk of interspecies transmission mediated by milk, a new vaccine platform capable of responding agilely to viral mutations and inducing local immunity was urgently needed.
Key Findings
Researchers developed a messenger RNA-lipid nanoparticle (mRNA-LNP) vaccine encoding the hemagglutinin (HA) protein of a representative circulating strain (A/dairy cattle/Texas/24-008749-002/2024) isolated from infected dairy cows in Texas, USA. They then evaluated immunogenicity and protective efficacy by assigning eight lactating cows to either a vaccine-administered group or a saline-treated control group (four cows each). The test group received two intramuscular doses of the vaccine, followed by a challenge experiment in which the virus was injected into the breast after a certain period.
High titers of HA-reactive and neutralizing antibodies were induced in the serum of vaccinated cows. It was also confirmed that HA-specific antibodies were produced not only in the blood but also in the secreted milk. Analysis following the viral challenge showed that the peak viral RNA shedding in milk in the vaccinated group decreased to approximately 1/1,000th of that in the control group. As viral replication was suppressed, vaccinated individuals showed a significantly lower frequency of clinical mastitis and a substantial reduction in fibrotic damage to mammary tissue. This indicates that the humoral immune response was delivered to the local breast area, thereby preventing infection damage.
Significance and Outlook
This trial is the first case to demonstrate that the mRNA-LNP platform can rapidly establish effective protective immunity against infectious diseases in large animals, including cattle. The speed advantage of mRNA, which enables the design and production of vaccines carrying target antigens within weeks of securing pathogen genetic sequences, opens the possibility of its direct application to livestock disease prevention. The result of suppressing viral shedding in crude oil by more than 3 log units directly contributes to blocking transmission between individuals within barns and reducing the risk of viral exposure for livestock workers and processing environments.
Practical challenges remain. The ultra-low temperature cold-chain storage requirements (down to dozens of degrees below zero) and cost issues associated with large-scale farm vaccination are cited as obstacles to the widespread adoption of livestock vaccines. As this was a small-scale proof-of-concept study involving eight cows, follow-up verification is required to identify the duration of sustained immunity and the efficiency of herd immunity formation in diverse rearing environments and large-scale populations.
Highly pathogenic avian influenza (HPAI) clade 2.3.4.4b H5N1 virus has recently emerged in dairy cattle in the USA, leading to mastitis and sharp reductions in milk production. The main site of H5N1 viral replication is the mammary tissue rather than the respiratory tract and viral transmission between animals is thought to occur through viral shedding in milk. Here, we generate an mRNA-lipid nanoparticle (mRNA-LNP) vaccine encoding the hemagglutinin (HA) of A/dairy cattle/Texas/24-008749-002/2024, representative of circulating bovine H5N1 viruses, and assess its immunogenicity and efficacy in lactating dairy cows. Eight cows were divided into vaccinated and control groups, receiving two intramuscular doses of the vaccine or saline, followed by intramammary viral challenge. Vaccination elicited HA-reactive and neutralizing antibodies in serum and HA-reactive antibodies in milk. Following viral challenge, vaccinated cows had ~1,000-fold lower peak viral RNA in milk and a lower occurrence of mastitis and mammary fibrosis.
The dairy industry is suffering massive economic damage due to sharp declines in milk production and mass infections mediated by milking equipment. This vaccine technology can be deployed immediately in a 'ring vaccination' format at the farm level upon viral entry, serving as a shield to minimize mastitis outbreaks and milk disposal losses during the early stages of infection.
Furthermore, it contributes to reducing the possibility of viral mutations or interspecies transmission to humans via unpasteurized raw milk at the source. As the mRNA platform, previously limited to human vaccine development, expands into livestock and agricultural disease control infrastructure, it marks a practical turning point in establishing a 'One Health' surveillance and response system capable of preemptively addressing zoonotic diseases.