Dawood and colleagues provide an important insight into influenza A(H5N1) infections and the surveillance tools needed for pandemic preparedness. Through rigorous review of international literature and careful molecular and serologic confirmation in 16 cases outside of the US, the authors document that influenza A(H5N1) infections among humans do not always present with severe illness, that asymptomatic infections occur, and in some settings, there is probable person-to-person transmission. This finding challenges the traditional perception that influenza A(H5N1) infection among humans is almost invariably symptomatic and severe.

The urgency of this message is underscored by recent events in the US. Since March 2024, influenza A(H5N1) clade 2.3.4.4b has spread widely among dairy cattle, with confirmed infections in more than 800 herds across at least 16 states. High viral titers have been detected in raw milk and viable virus has been recovered from mammary tissue and milking equipment. Spillover into, and transmission among, other mammals has been documented, including cats, dogs, mice, wild carnivores, marine mammals, and swine. Human cases have been confirmed in multiple states, and as of mid-2025, approximately 70 cases have been officially reported, most with mild illness but including at least 1 death. The report from Dawood and colleagues thus challenges the notion that there has been no human-to-human transmission related to these events. It also highlights a critical gap in many national and global surveillance systems, which tend to focus on the detection of symptomatic illness rather than infection, and underscores the importance of carefully examining clusters where limited transmission may occur.

The implications are substantial. If asymptomatic infections are occurring, transmission chains can go undetected, giving the virus opportunities to adapt and spread widely before an emerging pandemic is recognized. These silent events will not be captured by systems that rely primarily on symptom-based case finding. Dawood et al1 provide a strong evidence base for expanding the scope of influenza surveillance to include molecular and serologic testing of individuals at higher risk of exposure, whether or not they are experiencing symptoms, as well as testing of contacts of infected persons. This is particularly important for pathogens with pandemic potential, where early detection is essential for containing spread before it becomes sustained.

With regard to the dairy cattle–associated outbreak, the cases reviewed by Dawood et al suggest that cases could be significantly underestimated. Several investigations have detected antibodies to influenza A(H5N1) among veterinarians and dairy workers who had contact with infected cattle. In some studies, up to 7% of those tested had serologic evidence of infection, and about half of those individuals reported no symptoms. In contrast to the cases in the report by Dawood et al, these cases now arise from within the US. They point to a gap between what surveillance systems capture and the true scope of infection and highlight the need to strengthen, not curtail, surveillance and reporting.

Both human and animal public health scientists from the US Department of Agriculture, US Department of Health and Human Services, Centers for Disease Control and Prevention, US Food and Drug Administration, and the National Institutes of Health responded to the dairy cattle outbreak with valuable laboratory analyses, situational assessments, and guidance for occupational health. However, the operational rollout of surveillance measures revealed vulnerabilities. Asymptomatic testing of exposed workers was not initiated quickly, early human surveillance was limited in scope, and public communication about findings was delayed. Bulk tank milk testing was piloted months after initial detection of the virus in cattle and only later scaled more broadly. Environmental sampling around farms and equipment was intermittent rather than routine.

The persistence of influenza A(H5N1) in wild birds, its ongoing adaptation in mammals, and its repeated incursions into human populations make it clear that the threat does not subside when immediate headlines fade. The systems to detect and track such threats, whether influenza A(H5N1) or other high-threat pathogens, must be active in noncrisis periods, not built ad hoc in the middle of an outbreak. The experience of the past year shows the risk of relying on temporary, reactive measures rather than sustaining integrated, One Health surveillance capacity as a matter of routine.

Occupational cohorts at elevated risk of exposure, such as farmworkers, veterinarians, wildlife biologists, and laboratory staff, should be part of ongoing molecular and serologic surveillance programs. Animal, human, and environmental testing data should be linked and shared in real time between agricultural, public health, and environmental agencies. Laboratory and field investigation capacity must be maintained and exercised regularly, so that rapid response is possible when a novel pathogen emerges. Clear and timely communication of findings, including of asymptomatic infections, builds trust and enables effective coordination with state, national, and global partners.

Policymakers and public health leaders should recognize that the cost of maintaining such systems is small compared with the economic, health, and societal costs of uncontrolled spread. Surveillance is not only a tool for crisis response; it is the foundation of prevention. It must be designed to detect early, track comprehensively, and respond decisively, whether the cases are symptomatic or silent. Only with early warning can safe and effective vaccines be readied in time to get ahead of a pandemic.

Dawood and colleagues have provided timely and compelling evidence that asymptomatic human infections with influenza A(H5N1) occur and can be detected with the right tools. The recent US outbreak in dairy cattle has shown what is at stake when those tools are not applied broadly and routinely. For the new leadership at the Centers for Disease Control and Prevention, and for global public health officials, the opportunity now is to close the gap between what the science tells us and what the systems deliver. The threat of influenza A(H5N1) and other high-consequence pathogens will remain. Our surveillance, preparedness, and response capabilities must remain as well, always ready to detect and contain the next emergence before it becomes the next pandemic.