In the nearly nine months since the first human case of bird flu was detected in the United States, the virus has continued to spread.

The outbreak infected hundreds of herds and millions of birds before it spread to humans. As of Jan. 6, there have been 66 human cases of bird flu reported in 10 states, according to data from the Centers for Disease Control and Prevention (CDC).

Almost all confirmed cases involve direct contact with infected cattle or infected livestock.

On Tuesday, the first death of a human bird flu patient was reported in Louisiana. The patient was over the age of 65 and had underlying medical conditions, according to health officials.

The CDC says there is currently no evidence of human-to-human transmission and the risk to the general public is low.

However, public health experts say they are worried the virus could mutate and become more transmissible, amplifying the need to ramp up testing and to stockpile vaccines.

Dr. Tony Moody, a professor of pediatrics and infectious diseases specialist at Duke University, said the fact that cases have yet to pass from human to human is “both reassuring, but not completely reassuring.”

He told ABC News, “What we’re concerned about is that, eventually, we might get a variation of this strain that could pass from person to person. That’s really what we’re going to need to see, I think, to get substantial human cases and the potential for a new pandemic strain.”

He added, “So, in terms of peering into the crystal ball for 2025…I think the concern is whether or not we’re going to see something change that will turn it into a pandemic strain that could then really be a problem,” he added.

Fears of mutation or a combination virus

One fear experts have is that the virus will continue to mutate in a way that will cause more human-to-human transmissibility. The experts say that every new human case of bird flu allows the virus an opportunity to mutate.

Recent CDC data found mutations in samples of bird flu collected from the Louisiana patient. What’s more, the mutations were not found in poultry samples collected on the patient’s property, suggesting the changes appeared after the patient became infected.

Moody said that because the virus has not yet mutated in a way to spread more easily between humans, he’s not sure if or when it will happen.

“Given the number of cows that have been infected, the number of birds that have been infected and the fact that the virus essentially mutates every time it replicates, I’m kind of surprised that the mutations that they’re talking about haven’t happened yet,” he said. “So, I actually think there’s a bigger barrier to it becoming a real problem.”

Dr. Peter Hotez, co-director of the Texas Children’s Hospital Center for Vaccine Development and dean of the National School of Tropical Medicine at Baylor College of Medicine, said he believes there is a more likely scenario of the virus becoming more transmissible: an individual getting infected with bird flu and seasonal influenza at the same time.

He said this could lead to the virus “reassorting” to produce a hybrid, or recombinant, virus that could then transmit more easily from person to person.

“Everyone’s focusing on the potential for mutation; that is a serious concern for some,” he told ABC News. “The greater probability is that there could be a reassortment, what could ignite the pandemic or an epidemic.”

The experts say there is no evidence the virus is currently heading towards an epidemic or pandemic, but there has already been one case of severe disease.

Different genotypes, or genetic makeup of the virus, means there could more severe cases.

“What we’ve seen with [bird flu] in the United States is that the particular genotype that’s associated with dairy cows has primarily caused more mild disease in people,” Dr. Meghan Davis, an associate professor of environmental health and engineering at Johns Hopkins Bloomberg School of Public Health, told ABC News.

“What we’ve seen with the case in Louisiana … is caused by a different genotype, one that has been circulating in the wild birds, and these are much more severe cases,” she continued. “This highlights the ability of avian influenzas to cause a wide variety of disease … and I think it is possible that we’re going to see that moving forward.”

Making testing more available

The U.S. has begun ramping up testing with the U.S. Department of Agriculture issuing a federal order for raw milk samples nationwide to be collected and tested and the Food and Drug Administration announcing it is collecting samples of aged raw cow’s milk cheese to be tested.

However, for 2025, Hotez said he believes testing needs to be made more readily available to physicians, especially during flu season.

He said there are likely cases of bird flu going undiagnosed, and testing made more available in health care settings would catch those flying under the radar.

“I think one of the problems that we have, especially as we move into influenza season, there’s the risk that, if you’re a physician, if they want to do influenza testing, they’re only really testing for the usual seasonal influenza, they’re not testing for [bird flu],” he said. “Otherwise, we’re never going to fully know the actual extent of the problem.”

Stockpiling bird flu vaccines

In early July, the U.S. government awarded Moderna $176 million to develop and test a bird flu vaccine using mRNA technology, which is the same technology used for the COVID vaccine.

In October, federal health officials announced they were providing $72 million to vaccine manufacturers to help ensure currently available bird flu vaccines are ready to use, if needed.

There are currently no recommendations for anyone in the U.S. to be vaccinated against bird flu, but experts say that could change if the virus becomes more transmissible.

Moody said clinical trials for new vaccines are being conducted and there are already bird flu vaccines in a stockpile maintained by the U.S. government that have previously been licensed by the FDA.

However, these three vaccines were formulated to protect against older strains of bird flu so there are questions about their protectiveness.

“One of the difficulties in making a stockpile is you’re trying to predict the future. Picking which influenza is going to be a problem is always the difficult bit,” Moody said. “So, I think that those vaccines that are in the stockpile, based on the data that I’ve seen, have a pretty good chance of being helpful. Whether or not they’ll be the answer that’s a that’s a tougher question to address.”

He said the U.S. is in a better position currently to address bird flu if it becomes an epidemic or pandemic than the country was to address COVID in 2020.

“We know how to do this. We know how to make these vaccines. We know how to get everything rolled out, and so I think we are in a better position today,” Moody said.