H5N1 Incidence Continue to Stress Need for Broad Surveillance

Although there have been no federal updates on the spread of H5N1 since September 30, due to the government shutdown, updates made just prior to that, along with continuing reports of new H5N1 avian flu outbreaks in poultry on commercial farms are showing that the virus is continuing to plague some areas and the potential for human transmission continues.

The latest were CIDRAP-relayed outbreaks in Iowa, Minnesota, and Wisconsin commercial poultry farms, with the Iowa and Minnesota outbreaks being the eighth poultry outbreak in each state this year, and Wisconsin’s commercial flock outbreak impacting over a half million birds.

In relation to mammal and human transmission, on September 30, APHIS published the latest update on detections of highly pathogenic avian influenza in mammals showing detections in both wild and domestic animals across the US, with the Southeast being the least impacted, and Colorado having the highest density. In addition, two articles show the potential for the evolution of transmission to humans.

• In studying the genetics of H5N1 strains that have infected humans, CDC detected mutations that developed in a human with a severe bird flu case in early 2025. It is theorized that these make the strains more likely to infect humans in the future. As of July 22, 2025, 70 human cases of HPAI had been identified in the US since 2024, primarily from exposure to infected dairy cows and poultry.
• A JAMA article discussed the 2024 incidence of H5N1 detected in pigs in Oregon.  Although the pigs sharing of water, housing, and equipment with infected poultry likely facilitated the virus’ transmission, the incidence raises concerns because pigs are sometimes referred to as “mixing vessels” for influenza viruses because they can be infected by such viruses from birds, humans, and other animals and allow for reassortment of the viral genetic material. This could permit the virus to potentially be more infectious to humans.

While H5N1 human infection is still considered to be low risk, the realities of continuing outbreaks, the human mutations, and the pig infections stress the need for continued broad surveillance.

Public Health News:

• The CDC has updated its adult and child immunization schedules to emphasize individualized decision-making for COVID-19 vaccination and to recommend that toddlers receive the chickenpox vaccine separately from the combined measles, mumps, rubella, and varicella (MMRV) shot. These changes reflect recent recommendations from the CDC’s Advisory Committee on Immunization Practices (ACIP). The new guidance moves away from blanket COVID-19 booster recommendations, instead encouraging discussions between patients and healthcare providers based on personal risk factors. For toddlers, the update is based on evidence showing that the combined MMRV vaccine doubles the risk of febrile seizures in young children without offering added protection against chickenpox.
• The Ebola outbreak in the DRC seems more contained, likely due to aggressive public health responses, including vaccination among healthcare workers and their contacts. 
• A recent WHO report on Chikungunya highlights a general increase in cases globally in 2025. The Americas region has reported the highest number of cases, followed by the European region, with most illnesses reported from French overseas departments in the Indian Ocean. So far this year, more than 445,000 cases and 155 deaths have been reported from 40 countries. Transmission is speculated to occur from infected travelers which leads to cases among the local population with limited immunity. 
• Incidence of Mpox spiked in Chicago over the summer, with 104 cases reported since June 1, representing a 96% increase over 2024 and a 160% increase over 2023. In response, the public health department is continuing surveillance and sponsoring vaccination clinics in October.
• The CDC has been studying the genetics of H5N1 strains that have infected humans and have detected mutations that developed in a severe human case. They theorize that these make the strains more likely to infect humans in the future. 61 human infections have been reported to date in 2025 and while there is no evidence of human-to human transmission, surveillance remains important.  
• The CDC has published a report on routes of infection for Influenza A viruses. While respiratory infections are by far the most common, they also detected a very low level of transmission associated with consuming raw milk or meat products contaminated with the virus that led to GI symptoms. They caution that this oral transmission route is very rare but cannot be dismissed. 
• A JAMA article published on the incidence in 2024 of H5N1 detected in pigs in Oregon. The report describes that the virus was likely transmitted to the pig from infected poultry on the same farm, which shared equipment and water sources, though the infected pigs were asymptomatic. This is potentially concerning since pigs are sometimes referred to as “mixing vessels” for influenza viruses because they can be infected by such viruses from birds, humans, and other animals and allow for reassortment of viral genetic material. This could permit the virus to potentially be more infectious to humans. To date, this has not occurred, but this reality stresses the need for continued broad surveillance.