Here's how U.S. health officials are responding to bird flu in humans after second case

U.S. health officials are monitoring and preparing to combat bird flu in humans, even as they emphasize that the risk to the general public remains low. 

A strain of bird flu called H5N1 has been confirmed in dairy cows across nine U.S. states, as well as in two people, amid a global outbreak among poultry and other animals. The latest case was announced Wednesday in a dairy farm worker in Michigan. A child in Australia was also recently infected with bird flu, the country announced Tuesday.

H5N1 has been spreading among more animal species worldwide since 2020, but its detection in U.S. livestock earlier this year was a twist health officials did not expect. In rare cases, bird flu viruses spread to humans and can cause mild to severe symptoms that can require hospitalization. 

There is currently no evidence that H5N1 is spreading from person to person. The Centers for Disease Control and Prevention has also said the risk of infection is higher among farmworkers than in the general population. 

Still, the U.S. government, along with state and local health departments, are monitoring new and emerging infections among humans and animals. Federal agencies in the U.S. and elsewhere have also tracked the H5N1 virus for years to monitor its evolution. 

The U.S. government has long stockpiled vaccines and drugs to be used in a possible bird flu pandemic. Last week, it started the process of preparing nearly 5 million doses of vaccines expected to be well-matched against H5N1, among other efforts to respond, the Health and Human Services Department confirmed to CNBC. 

Some infectious disease experts told CNBC the U.S. government appears to be generally prepared if bird flu begins to spread more widely and easily to humans, especially compared with how equipped the country was for the Covid pandemic. The experts said most of the necessary tools are already on hand but the government must ensure it deploys them effectively, if needed. 

"There's a lot of pieces that are already in place that help us understand that we can respond to this faster," said Dr. Andrew Pekosz, a professor at the Johns Hopkins Bloomberg School of Public Health. "As is always the case, though, it's about the efficiency of our responses, right? We know what we can do. We just have to be able to do it effectively."

The latest human infection, in the Michigan dairy worker, is not a surprise, according to both experts and the government. The CDC said Wednesday that similar cases in humans could be identified because high levels of the virus have been found in raw milk from infected cows.

The U.S. government currently has two vaccine virus candidates that it believes are a good match for H5N1. Those candidates are weakened versions of a virus that trigger a protective immune response against it in the body and can be used to produce vaccines.

Both of the candidates are already available to manufacturers, according to the CDC. The government last week started the process of manufacturing 4.8 million doses of those human vaccines in case they are needed, HHS confirmed. 

Pekosz called those doses a "first line of defense in case we do see some human-to-human transmission." He said that number is enough to stem an outbreak in its early stages, which could include vaccinating farm workers and some health-care workers. 

But he said far more are needed for the more than 300 million people in the U.S. if the virus spreads widely among humans. 

"Five million doesn't really get us very far. It's just a quick start," Pekosz said. 

U.S. health officials said May 1 that the government could ship more than 100 million doses of human bird flu vaccines within three to four months if needed, NBC News reported. 

Notably, people will need two doses of a vaccine, meaning that 100 million doses is enough for only 50 million people. That suggests the U.S. would need roughly 600 million shots if it wanted to vaccinate the entire population. 

The government faces a difficult decision on how many shots to prepare, especially since it takes a few months to make them.

"It's either too little or too much. For example, if you make too much food, then a lot of food goes to waste," said Dr. Peter Chin-Hong, an infectious disease physician at UCSF Health. "That's really the whole big conundrum now with a vaccine whenever you have a potential threat. It's the high cost and high-risk aspects."

Chin-Hong said misinformation and vaccine hesitancy after Covid makes that decision all the more challenging. But he said he believes "you can never really invest too much" in preparing for potential pandemics, especially at a time when climate change, population growth and other factors make them increasingly likely to happen.

The Food and Drug Administration would need to approve bird flu vaccines before they roll out. But Pekosz said that will likely be a "rapid procedure" since the FDA is accustomed to clearing seasonal flu vaccines, which are made using the same manufacturing process as bird flu shots. 

U.S. health officials are also in talks with messenger RNA vaccine makers about potential bird flu shots for humans. Few details have been shared about those negotiations, but HHS said a final announcement is expected soon. 

Unlike traditional flu shots, mRNA works by teaching cells to produce a harmless piece of a virus, which triggers an immune response against certain diseases. It is the same technology both Pfizer and Moderna have used in their Covid vaccines. 

Chin-Hong said mRNA vaccines could be updated more quickly to match the currently circulating strains of the bird flu. But he said those vaccines have their own challenges, such as needing to be stored at extremely cold temperatures.

In a statement to CNBC, Moderna confirmed that it is involved in negotiations with the government regarding its experimental pandemic influenza shot, mRNA-1018. It targets the exact strain of the virus responsible for the outbreak in dairy cattle. 

The biotech company began testing that shot in an early- to mid-stage trial last summer.

Pfizer declined to confirm negotiations with the government. The company said it is continuing to monitor the spread of H5N1 and study its mRNA-based pandemic influenza vaccine candidates in an early trial. 

The CDC and its partners, including state and local health departments, use multiple surveillance systems to monitor seasonal influenza and other illnesses. They also have specialized methods to detect and monitor new flu viruses. 

Seasonal influenza spreads mostly among humans with predictable peaks during the year, while bird flu spreads mostly among wild birds and other animals.

The CDC said it is looking for the spread of H5N1 to or among people in areas where the virus has been identified in animals or humans. So far, the agency has found "no indicators of unusual influenza activity in people," including H5N1, according to an update on the agency's site from last week. 

The CDC also performs ongoing analyses of seasonal and new influenza viruses to identify genetic changes that might allow for them to cause more serious infections in humans, spread more easily to and between people or become less susceptible to vaccines and drugs.

While there is robust testing on the federal, state and local levels, it is far more difficult for an average person to self-screen and get diagnosed for bird flu like they can for Covid, Chin-Hong said. That's "the big barrier, particularly in the populations that are getting affected now," he said.

Chin-Hong is referring to farm workers, a large share of whom are immigrants, who may struggle to navigate the U.S. health system due to language barriers and health-care access. 

If people do contract the virus, there are a few FDA-approved antiviral drugs for seasonal flu that can be used for bird flu. That includes Tamiflu, which is an oral prescription medication that should be taken within 48 hours of experiencing symptoms. 

A Texas dairy farm worker who was diagnosed with bird flu in March was treated with an antiviral drug and recovered, according to a CDC report.

But Pekosz said the antiviral drugs in the nation's stockpile are likely not enough for the vast majority of the population, so manufacturers may be asked to scale up supply.

The average person can protect themselves from bird flu by avoiding any living or dead animals that might be infected, such as livestock or chickens, according to Francesca Torriani, infectious disease specialist with UC San Diego Health.

People who need to make contact with those animals should wear the appropriate mask and eye protection and wash their hands afterward.

Torriani added that pasteurized milk and cheese are likely safer to consume than raw dairy products since the pasteurization process kills harmful bacteria.