What you need to know about human cases and the vaccine

U.S. health officials are preparing to monitor and respond to bird flu in humans, while stressing that the risk to the general public remains low.

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

H5N1 has spread to more animal species around the world since 2020, but its detection in U.S. livestock earlier this year was a development health officials did not anticipate. In rare cases, the avian flu virus can infect humans, causing mild to severe illness that may require hospitalization.

There is currently no evidence that H5N1 is transmitted from person to person, and the Centers for Disease Control and Prevention has said agricultural workers are at higher risk of infection than the general population.

Still, the US government works with state and local health departments to monitor for emerging infectious diseases in humans and animals, and federal agencies in the US and other countries have also been following the H5N1 virus for years to monitor its evolution.

The US government has long been stockpiling vaccines and medicines in preparation for an avian flu pandemic, and last week the government began preparing about 5 million doses of a vaccine that is expected to be well-matched to the H5N1 strain as part of its response, the Department of Health and Human Services confirmed to CNBC.

Some infectious disease experts told CNBC that the US government appears generally prepared if bird flu begins to infect humans more widely and easily, especially compared to how the US was prepared for the COVID-19 pandemic. Experts said most of the necessary tools are already at hand, but the government must deploy them effectively when needed.

“There are a lot of pieces already in place that help us understand we can respond more quickly,” said Dr. Andrew Pecos, a professor at the Johns Hopkins Bloomberg School of Public Health. “But as always, our response is about efficiency. We know what we can do, we just need to be able to execute it effectively.”

Experts and governments say the latest human infections in Michigan dairy workers are not surprising: The CDC said Wednesday that high levels of the virus have been found in raw milk from infected cows, allowing it to identify similar cases in people.

The US government currently has two vaccine virus candidates that it believes are well-matched to the H5N1 strain — weakened versions of the virus that can trigger a protective immune response in the body and can be used to make a vaccine.

Both candidate vaccines have already been delivered to manufacturers, according to the CDC, and the government has begun manufacturing 4.8 million doses of the vaccines for humans as needed, HHS confirmed last week.

Pecos called these vaccinations “a first line of defense if person-to-person transmission occurs.” He said the numbers are enough to stop the spread in the early stages and could also include vaccinating farmworkers and some health care workers.

But he said far more vaccines would be needed to cover the more than 300 million people in the United States if the virus spread widely among humans.

“Five million won’t get you very far. It’s just a fast start,” Pecos said.

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

It’s important to note that the vaccine requires two doses, meaning 100 million doses would be enough for only 50 million people, meaning the US would need roughly 600 million doses to vaccinate its entire population.

Vaccines take months to manufacture, so governments face tough decisions about how many doses to stock.

“You either have too little or too much. For example, if you make too much food, a lot of food goes to waste,” said Dr. Peter Chin-Hong, an infectious disease physician at UCSF Health. “Anytime there’s a potential threat, there’s a really big conundrum right now with vaccines, which is the high cost and high risk aspect.”

Chin-Hong said post-COVID misinformation and vaccine hesitancy make the decision even tougher, but he said he believes “you can never invest too much” in preparing for a potential pandemic, especially now that factors like climate change and population growth make it more likely.

Avian flu vaccines must be approved by the Food and Drug Administration before they can be marketed, but Pecos said approval is likely to be a “fast track” because the FDA is accustomed to approving seasonal flu vaccines, which are made using the same manufacturing process as avian flu vaccines.

U.S. health officials are also in talks with messenger RNA vaccine manufacturers about a possible bird flu vaccine for humans. Few details have been released about the talks, but the Department of Health and Human Services said a final announcement is expected soon.

Unlike traditional flu vaccines, mRNA induces cells to produce harmless pieces of the virus that trigger an immune response against a specific disease. Pfizer and Moderna It is used in the new coronavirus vaccine.

Chin Hong said mRNA vaccines can be updated more quickly to suit currently circulating strains of bird flu, but he said these vaccines come with their own challenges, such as the need to be stored at extremely cold temperatures.

Moderna confirmed in a statement to CNBC that it is in talks with the government about an experimental pandemic flu vaccine, mRNA-1018, that precisely targets the strain of the virus causing the outbreak in dairy cows.

The biotechnology company began testing the vaccine in early- to mid-stage clinical trials last summer.

Pfizer declined to confirm any negotiations with the government. The company said it continues to monitor the spread of H5N1 and is researching early testing of an mRNA-based pandemic influenza vaccine candidate.

CDC and its partners, including state and local health departments, use multiple surveillance systems to monitor seasonal influenza and other illnesses, and we also have specialized methods for detecting and monitoring new influenza viruses.

Seasonal influenza spreads mainly among humans and has predictable peaks throughout the year, while avian influenza spreads mainly among wild birds and other animals.

The CDC said it is monitoring the spread of the H5N1 virus to or among humans in areas where it has been identified in animals and humans. So far, the agency has “not found any indications of unusual influenza activity in humans,” including the H5N1 virus, according to an update on its website last week.

CDC also continues to analyze seasonal and novel influenza viruses to identify genetic changes that may lead to the viruses causing more severe infections in humans, making them more easily transmitted between or among people, or making them less susceptible to vaccines or drugs.

Chin-Hong said that while testing is widespread at the federal, state and local levels, it’s much harder for the general public to self-test and get a diagnosis for avian flu, as it is for the new coronavirus. “That’s a big barrier, especially in the populations where we’re seeing the current spread,” he said.

Chin Hong is referring to farmworkers, many of whom are immigrants and who may struggle to understand the U.S. health care system due to language barriers and access to care.

If humans become infected with the virus, there are several FDA-approved antiviral drugs that work against seasonal influenza and can be used against bird flu, including Tamiflu, an oral prescription drug that must be taken within 48 hours of symptoms appearing.

A Texas dairy worker who was diagnosed with avian flu in March was treated with antiviral drugs and recovered, according to a CDC report.

But Pecos said the national stockpile of antiviral drugs likely won’t be enough for the majority of the population, and manufacturers may be asked to increase supplies.

The public can protect themselves from bird flu by avoiding live and dead animals that may be infected, such as farm animals and chickens, said Francesca Torriani, an infectious disease specialist at the University of California, San Diego Health School.

Anyone who needs to come into contact with these animals should wear appropriate masks and eye protection and wash their hands after contact.

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