(WASHINGTON) — Bird flu is continuing to spread in animals across the United States more than a year after the first human case was detected.

Since then, at least 70 people have fallen ill and at least one death was recorded in Louisiana, according to the Centers for Disease Control and Prevention.

The number of confirmed cases in humans has held steady for almost two months, but hundreds of dairy cows continue to be infected and raw milk samples in several states have tested positive for bird flu, according to federal health officials.

There is currently no evidence the virus is spreading between people, and the CDC has said the risk to the general public is low. However, some experts told ABC News fear the virus could still mutate or adapt to become more severe or transmissible.

Here’s the latest to know about the virus and current situation.

Bird flu in the U.S.

Bird flu, or avian influenza, is an infectious viral disease that primarily spreads among birds and is caused by infection with Avian Influenza A viruses

In March 2024, bird flu was reported in U.S. dairy cows for the first time. As of Friday, the virus has infected more than 1,000 herds across 17 states, according to the U.S. Department of Agriculture (USDA).

The CDC confirmed the first human case in April 2024 in a Texas dairy worker who was exposed to cows presumed to be infected. This is believed to be the first instance of mammal to human spread of the H5N1 strain.

Bird flu has also been causing outbreaks in poultry, leading to human cases among U.S. poultry farm workers and culling operations workers.

Three human cases have had no known or identifiable exposure to the virus.

Dr. Tony Moody, a professor of pediatrics and in immunology at Duke University School of Medicine, said there has been so much transmission of bird flu in animals that he wonders if mass immunity is far off.

“In terms of the cattle population and other animal reservoirs, I’m starting to wonder exactly how many more cases we’ll see because, at this point, we’re probably heading toward — and pun is intended here — herd immunity,” he told ABC News.

Moody said there is currently no evidence of human-to-human transmission, which he says raises the question of whether or not H5N1 is likely to make that jump.

What is the U.S. doing to fight bird flu?

According to the USDA, the agency is investing $1 billion to fight bird flu, including $500 million for biosecurity measures, $400 million in financial relief for affected farmers and $100 million for vaccine research.

Between March 2024 and now, the CDC said it — along with state and local health departments — have monitored at least 16,600 people exposed to infected animals and tested at least 880. Meanwhile, USDA is responsible for testing livestock herds.

Moody said ramping up testing on both sides would give public health workers better situational awareness.

“I think the real question comes down to: how much do we want to test animals and people in order to be able to nail down transmission events and really understand how frequently this is happening?” Moody said, “I would personally like to see better surveillance and more coordinated surveillance.”

He said he understands this might not be possible due to the allocation of limited resources, but it would provide a better national picture.

“I think that the problem we have right now is that we have an incomplete view because testing of animals falls under one department, testing of people falls under a different department,” Moody said. “They don’t necessarily communicate in real time with accurate information and, the two agencies in question here, they’ve got very different purposes.”

Dr. Dean Blumberg, chief of the division of pediatric infectious diseases at the University of California, Davis Health, said he is worried that there has been a curtailing of testing and surveillance.

“If we don’t have the data then we don’t know what next steps to take,” he told ABC News. “There is increased likelihood that there will be increased spread among animals and humans and, by the time we become aware of increased transmission, then it may be too late for successful mitigation.”Under the USDA’s National Milk Testing Strategy to test raw milk samples for bird flu, the agency has identified at least seven affected states.

Meanwhile, the Food and Drug Administration announced last year it was beginning to sample aged raw cheese to test bird flu, with early results showing most samples were negative.

On the vaccine front, the U.S. has licensed three bird flu vaccines, targeting the H5N1 strain, which are being held in a national stockpile. They are not available to the public and would only be distributed in case of an emergency.

Last year, the World Health Organization it launched an initiative to help accelerate the development of a human bird flu vaccine using messenger RNA (mRNA) technology.

Earlier this year, Moderna was awarded approximately $590 million from the federal government to help speed up the development of an mRNA-based bird flu vaccine, alongside other influenza vaccines.

What we don’t know

Although there is no evidence of human-to-human transmission yet, or that the virus has mutated to become more infectious, Moody said he still worried about mutations and adaptations.

Earlier this year, a dairy cow was found to be infected with another type of bird flu for the first time, which experts have previously said is evidence that the virus is adapting.

“The thing about this virus is that it mutates every time somebody gets infected, right?” Moody said. “We know that there is an intrinsic rate of mutation that the virus has, and as with most mutations, the vast majority … don’t lead to any additional pathogenicity or transmissibility.”

He went on, “But the more cases that you have, whether that is in chickens or cows or people, the more of those random events are occurring and we know that eventually the virus will probably find a way to increase its transmissibility to people or increase some other property that makes it a problem.”

Moody said he is also concerned about reassortment, which is when a hybrid — or recombinant — virus, is formed. An example is an individual getting infected with bird flu and seasonal influenza at the same time and a hybrid virus forming as a result.

He clarified that there is no evidence this has happened yet, and that he believes the U.S. is in a better position to respond today if a pandemic-like situation arises, “but nature has a way of surprising us.”

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