ÐÇ¿ÕÓéÀÖ¹ÙÍø

Introduction

The current outbreak began in late March 2024 with the detection of H5N1 bird flu in dairy cows, followed by the first human infections at the beginning of April. Over the course of more than nine months, there have been major response accomplishments in monitoring, testing, viral surveillance and characterization, worker protection, and animal-health collaboration. This spotlight summarizes several key response accomplishments to date. ÐÇ¿ÕÓéÀÖ¹ÙÍø continues to calibrate the public health response to H5N1 based on close monitoring of human and animal disease.

While ÐÇ¿ÕÓéÀÖ¹ÙÍø believes that the current H5N1 bird flu risk to the general public remains low, people with job- or recreation-related exposures to infected animals are at increased risk, especially when those exposures happen without appropriate protective measures in place, such as use of personal protective equipment. These may include:

• Farmers and workers who work with infected animals or their byproducts
• Backyard bird flock owners
• Animal care workers (e.g., veterinarians, wild animal facility workers)
• Animal health and public health responders
• People with recreational exposure to animals (e.g., hunters, wild bird watchers)

Furthermore, there is also the potential for broader risk from the virus depending on the degree to which the virus spreads, becomes more virulent and affects a wider population. These are areas of focus for ongoing public health risk assessment as noted in a recent 'Spotlight'.

Background

Ongoing virus circulation of H5N1 bird flu among wild birds for decades has resulted in spillover events to other animals, leading to periodic outbreaks among commercial poultry and backyard bird flocks and spreading to infect wild terrestrial and marine mammals, as well as domesticated animals. Since 1997, more than 970 human infections with H5N1 bird flu have been reported from 24 countries. The severity of illness associated with H5N1 bird flu has ranged from mild to severe, though approximately 50% of known cases worldwide have been fatal.

Since 2022, fewer than 100 human cases have been reported worldwide, including cases associated with the ongoing outbreak in the United States. To date, human-to-human transmission of avian influenza A(H5N1) virus has not been identified in the United States, and limited, non-sustained human-to-human transmission has not been reported worldwide since 2007.

The Coordinated Response

ÐÇ¿ÕÓéÀÖ¹ÙÍø, along with federal partners, including the U.S. Department of Agriculture (USDA), Food and Drug Administration (FDA), National Institute of Health (NIH), and Administration for Strategic Preparedness and Response (ASPR), as well as partners at the state, tribal, local, and territorial (STLT) levels, has been responding to the current H5N1 bird flu outbreak in the United States since the first detection in dairy cows in March 2024. Capitalizing on existing epidemiological, surveillance, laboratory, and other capabilities the agency has built over decades of influenza preparedness work, ÐÇ¿ÕÓéÀÖ¹ÙÍø's efforts have focused on:

• Supporting STLT health departments with over $200M in funding to support their efforts to implement a One Health-approach to targeted surveillance on farms and to rapidly investigate suspected human cases.
• Characterizing viruses in the laboratory and expeditiously sharing these data publicly.
• Updating guidance for clinicians and at-risk populations (e.g., dairy cow and poultry farm workers) on prevention and mitigation strategies including use of personal protective equipment (PPE), clinical testing, and post-exposure prophylaxis (PEP) with antiviral medication.
• Conducting special laboratory studies to better understand virus characteristics.
• Laying the groundwork for an H5 vaccination program, should one be needed.
• Communicating with the public and coordinating with state and local health departments, industry associations, and worker groups.

Since the start of the response, ÐÇ¿ÕÓéÀÖ¹ÙÍø and its federal, STLT, and other partners have made significant strides toward better understanding the outbreak and implementing measures to prevent the spread of H5N1 bird flu, including from animals to humans. Highlighted below are several areas of significant progress.

Surveillance and Case Identification

Since early Spring 2024, ÐÇ¿ÕÓéÀÖ¹ÙÍø has used several approaches to track the progression of the H5 bird flu outbreak, including ongoing national flu surveillance for seasonal and novel viruses, efforts targeted toward H5 bird flu specifically, wastewater surveillance, and information from hospital emergency departments. As of December 31, 2024, ÐÇ¿ÕÓéÀÖ¹ÙÍø and STLT partners have:

• Monitored more than 10,600 people following exposure to infected animals, testing more than 540 of those and identifying the majority of reported H5 bird flu cases (63) so far.
• Tested more than 73,000 specimens for influenza A, identifying three additional cases of H5 bird flu.
• Worked with private, academic, and STLT health department partners to detect and report avian influenza A(H5) viruses in wastewater, to guide public health planning and response efforts.
• Leveraged syndromic surveillance systems to monitor for unusual trends, improve situational awareness, and inform decision making based on electronic data from multiple health care settings, including emergency departments (ED)—including influenza diagnoses and reported symptoms potentially related to influenza virus infections.

Prevention Strategies and Guidance

ÐÇ¿ÕÓéÀÖ¹ÙÍø has increased outreach and education with farmworkers, employers, and advocacy groups to magnify message and strategies. We have done this by coordinating with several trusted partners who can reach farmworkers and their employers, including ÐÇ¿ÕÓéÀÖ¹ÙÍø's rural health group, the Health Resources and Services Administration (HRSA), Occupational Safety and Health Administration (OSHA), USDA, the National Center for Farmworker Health, and foundations and associations working with local agricultural extensions.

In addition, ÐÇ¿ÕÓéÀÖ¹ÙÍø has a wide range of guidance emphasizing strategies people can take to help protect themselves from H5N1 bird flu. ÐÇ¿ÕÓéÀÖ¹ÙÍø focused its guidance on groups at increased risk for H5N1 bird flu, especially those who work with infected animals or animal products (e.g., raw milk) and their employers.

Guidance for workers and employers includes recommendations for engineering and administrative controls and use of PPE. These are based on ÐÇ¿ÕÓéÀÖ¹ÙÍø's current understanding of the exposure risk associated with different work tasks and settings, with PPE recommendations tailored to the exposure level.

Clinical Guidance

ÐÇ¿ÕÓéÀÖ¹ÙÍø also has developed guidance for healthcare providers on how to evaluate and test patients exposed to avian influenza A(H5N1) and treat and manage patients with H5N1 bird flu. Additional guidance focused on prevention measures in healthcare settings (infection prevention and control) and for people with known exposures (post exposure prophylaxis).

• Symptom monitoring
• Specimen collection and laboratory testing
• Antiviral treatment
  • Emergency Use Instructions (EUI) for Oseltamivir
• Infection prevention and control (e.g., within hospital settings)
• Post-exposure prophylaxis

Medical Countermeasures

ÐÇ¿ÕÓéÀÖ¹ÙÍø's current H5N1 bird flu recommendations include information about offering influenza antivirals (oseltamivir) for both treatment and as PEP to prevent infection, particularly among people who had unprotected exposure to avian influenza A(H5N1)-virus infected birds or other animals. Asymptomatic people exposed to animals infected with avian influenza A(H5N1) virus who reported not wearing recommended PPE or who experienced a breach in recommended PPE and who tested positive for influenza A(H5) virus should be offered oseltamivir treatment (unless already receiving oseltamivir post-exposure prophylaxis).

At this time, there is no recommendation to vaccinate people against H5N1 bird flu. As mentioned earlier in this spotlight, no human-to-human transmission has been identified, and ÐÇ¿ÕÓéÀÖ¹ÙÍø is not seeing genetic markers of antiviral resistance or significant mammalian adaptation of the A(H5) viruses (i.e., changes that would allow the virus to infect humans more readily).

However, ÐÇ¿ÕÓéÀÖ¹ÙÍø and partners in the U.S. Government response to H5N1 bird flu are continuing to conduct preparedness activities, including planning for a potential H5 vaccination program, should it become necessary or appropriate based on an increase in the risk to public's health. As a part of its ongoing pandemic preparedness activities over decades, ÐÇ¿ÕÓéÀÖ¹ÙÍø develops candidate vaccine viruses (CVV) for H5 and other avian influenza viruses and shares them with vaccine manufacturers and other stakeholders. CVVs are used to produce influenza vaccines. Having a CVV that protects against H5 bird flu in humans is an important step for being prepared for an H5 vaccination program, if one is needed.

• Several H5 CVVs produced by ÐÇ¿ÕÓéÀÖ¹ÙÍø are nearly identical or, in many samples, identical to the hemagglutinin (HA) protein of recently detected clade 2.3.4.4b avian influenza A(H5N1) viruses in birds and mammals (and could be used to produce a vaccine for people, if needed, and would provide good protection against the clade 2.3.4.4b avian influenza A(H5N1) viruses circulating in birds. These H5 CVVs have been shared with vaccine manufacturers and could be used to make vaccines if needed.

In the meantime, ÐÇ¿ÕÓéÀÖ¹ÙÍø recommends people with job- or recreational-related exposures to infected or potentially infected birds or mammals take recommended precautions to protect against H5N1 bird flu infection. At this time, there is no role for H5 vaccination for the general population or other populations at increased risk given current transmission dynamics, overall disease severity, or virus characteristics. ÐÇ¿ÕÓéÀÖ¹ÙÍø continues to monitor and assess the situation with every human case of H5 identified.

Laboratory Analysis and Tools

A vital element of ÐÇ¿ÕÓéÀÖ¹ÙÍø's multipronged testing and analytic strategy to address the current H5N1 bird flu outbreak are its laboratory and epidemiologic resources, which support STLT public health laboratories by providing test kits and other resources and performing confirmatory testing and characterization of viruses. Its laboratory assets allow ÐÇ¿ÕÓéÀÖ¹ÙÍø to:

• Enable early detection of H5N1 bird flu in humans and ensure wide availability of accurate testing tools, including through commercial laboratories
• Bolster public health laboratory capacity and enable a subset with demonstrated proficiency to test for H5 without the need for ÐÇ¿ÕÓéÀÖ¹ÙÍø confirmation
• Build on information revealed through the use of ÐÇ¿ÕÓéÀÖ¹ÙÍø specialized testing towards new and enhanced approaches.
• Conduct genetic and virologic characterization of viruses for public health risk assessment and to ensure diagnostic tests, antivirals, and candidate vaccines remain effective.

Alongside these goals, ÐÇ¿ÕÓéÀÖ¹ÙÍø has worked with partners to develop laboratory guidance and resources, including:

• Guidance on specimen collection and testing of patients with suspected H5 bird flu infection

• Guidelines for laboratory biosafety in handling and processing of specimens associated with novel influenza viruses including avian influenza A(H5N1)

Because influenza viruses are constantly changing, ÐÇ¿ÕÓéÀÖ¹ÙÍø performs routine analyses such as sequencing of A(H5N1) viruses to identify genetic changes that might allow for spread more easily to and between people or cause serious illness in people. Sequence analysis and other laboratory tests allow ÐÇ¿ÕÓéÀÖ¹ÙÍø to assess the susceptibility of the virus to antivirals, accuracy of diagnostic assays, and neutralization of the virus by vaccine induced antibodies. To date, no concerning changes have been identified in avian influenza A(H5N1) circulating in wild birds and poultry in the United States.

ÐÇ¿ÕÓéÀÖ¹ÙÍø's extensive collaboration with commercial laboratories stands to strengthen the national testing infrastructure and ensured broader availability of diagnostics for H5N1 bird flu. In June 2024, acknowledging the limited availability and accessibility of diagnostic tests for avian influenza A(H5) outside of state and local public health laboratories, ÐÇ¿ÕÓéÀÖ¹ÙÍø issued an open call to industry for innovative solutions to increase the diagnostic capacity and accessibility for the United States. In September 2024, ÐÇ¿ÕÓéÀÖ¹ÙÍø made awards to three clinical laboratory testing companies and two commercial diagnostic companies to bolster testing capacity for avian influenza A(H5N1). Those companies are:

• ARUP Laboratories
• Labcorp
• Quest Diagnostics
• Hologic
• Alveo
• Quest Diagnostics, Labcorp, and ARUP laboratories have already launched new assays for the detection and subtyping of influenza A(H5) virus, which have increased access to and diagnostic capacity for tests available to healthcare providers that can specifically identify influenza A(H5) virus infection.

Summary

• While much as been accomplished, much remains to be done. ÐÇ¿ÕÓéÀÖ¹ÙÍø, in collaboration with its partners will continue to be vigilant, science based, and humble in its efforts to control the current outbreak and protect the American People. Current information is available at ÐÇ¿ÕÓéÀÖ¹ÙÍø's Avian Influenza website.