What you need to know about human cases, vaccines

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

There is currently no evidence that H5N1 is transmitted from person to person. The Centers for Disease Control and Prevention 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, is monitoring new and emerging infections in humans and animals. Federal agencies in the United States and elsewhere have also been tracking the H5N1 virus for years to track its progress.

The U.S. government has long had stockpiles of vaccines and drugs intended for use in the event of a possible avian flu pandemic. Last week, it began the process of preparing nearly 5 million doses of vaccines that are expected to be well suited against H5N1, among other response efforts, the Department of Health and Human Services confirmed to CNBC.

Some infectious disease experts told CNBC that the U.S. government appears generally prepared if bird flu begins to spread more widely and more easily to humans, especially compared to how well the country is equipped for the Covid pandemic. Experts said most of the necessary tools are already available, but the government must ensure they are deployed effectively, if necessary.

“A lot of things are already in place that help us understand that we can respond more quickly,” said Dr. Andrew Pekosz, a professor at the Johns Hopkins Bloomberg School of Public Health. “But as is always the case, it’s a question of the effectiveness of our responses, isn’t it? We know what we can do. We just have to be able to do it effectively.”

The latest human infection in a Michigan dairy worker is no surprise, experts and the government say. 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 virus vaccine candidates that it says are a good match for H5N1. These 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 candidates are already available to manufacturers, according to the CDC. The government last week began the process of manufacturing 4.8 million doses of these human vaccines in case they are needed, HHS confirmed.

Pekosz called these doses “the first line of defense in case we see human-to-human transmission.” He said that number is enough to stem an outbreak in its early stages, which could require vaccination of farmworkers and some health care workers.

But he added that much more would be needed for the more than 300 million people in the United States if the virus spreads widely among humans.

“5 million doesn’t get us very far. It’s just a quick start,” Pekosz said.

U.S. health officials said earlier this month 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 100 million doses are only enough for 50 million people. This suggests that the United States would need around 600 million vaccines if it wanted to vaccinate the entire population.

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

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

He said misinformation and vaccine hesitancy post-Covid made this decision even more difficult. But Chin-Hong said he believes “you can never really invest too much” in preparing for possible pandemics, especially at a time when climate change, population growth and other factors make them more and more likely.

The Food and Drug Administration would need to approve avian flu vaccines before they are rolled out. But Pekosz said it would likely be a “quick process” since the FDA is accustomed to authorizing 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 makers about possible avian flu vaccines for humans. Few details have been shared about these negotiations, but HHS said a final announcement is expected soon.

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

Chin-Hong said mRNA vaccines could be updated more quickly to match strains of bird flu currently circulating. But he added that these vaccines present their own challenges, such as the need to store them at extremely cold temperatures.

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

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

Pfizer declined to confirm negotiations with the government. The company said it continues to monitor the spread of H5N1 and study its mRNA-based pandemic flu vaccine candidates in an initial 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 flu spreads primarily among humans with predictable peaks during the year, while avian flu spreads primarily among wild birds and other animals.

The CDC said it is looking for the spread of H5N1 to or among people living 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 humans,” including the H5N1 virus, according to an update posted last week on the agency’s website.

The CDC also conducts ongoing analyzes of seasonal and novel flu viruses to identify genetic changes that might allow them to cause more severe infections in humans, spread more easily between people, or become less susceptible to vaccines and to medications.

While there is rigorous testing at the federal, state, and local levels, it is much more difficult for the average person to self-screen and get a diagnosis for bird flu like they can for Covid. Chin-Hong said this was “the big obstacle, especially among the populations that are currently affected.”

Chin-Hong is referring to agricultural workers, many of whom are immigrants, who may have difficulty navigating the U.S. health care system due to language barriers and access to health care.

If people contract the virus, there are a few FDA-approved antiviral medications for seasonal flu that can be used for bird flu. This includes Tamiflu, a prescription oral medication that must be taken within 48 hours of symptoms appearing.

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 national stocks are probably not enough for the vast majority of the population, and so manufacturers may be asked to increase their supply.

The average person can protect themselves against bird flu by avoiding any living or dead animals that might be infected, such as livestock or chickens, according to Francesca Torriani, a professor of clinical medicine at the University of California, San Diego.

People who must come into contact with these animals must wear the appropriate mask and protective glasses and wash their hands afterward.

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