Outbreaks of avian influenza among dairy cows in several states, and at least one infection among a farm worker in Texas, have raised fears that the virus could be the next infectious threat to people.
The influenza virus, called H5N1, is highly pathogenic, meaning it has the ability to cause severe illness and death. But while its spread among cows was unexpected, people can contract the virus only through close contact with infected animals, not each other, federal officials said.
“These are actually people who are in environments where they might interact with cattle infected with this virus,” said Dr. Demeter Daskalakis, director of the National Center for Immunization and Respiratory Diseases at the Centers for disease control and prevention.
“The risk for most others is very low,” he added. “At the moment, our risk assessment has not changed, but if it does change, we will be quite prompt and transparent about it.”
Bird flu is often deadly among birds, but so far none of the infected cows have died. The only symptom found in the Texas patient was conjunctivitis, or conjunctivitis, also found in infected people during other avian flu epidemics.
The CDC and other agencies in the United States and elsewhere have been tracking H5N1 for years to monitor its evolution. Federal agencies have stockpiled vaccines and drugs for use in a possible avian flu epidemic.
“We are more ready for a flu pandemic than any other outbreak that could occur, any other pathogen,” said Rick Bright, chief executive of Bright Global Health, a consulting firm that focuses on improving responses to public health emergencies.
Dr. Bright led influenza preparedness at the Biomedical Advanced Research and Development Authority, or BARDA, the federal agency that supports vaccine and emergency drug research, for several years before serving as director of the agency from 2016 to 2020.
Here's what you need to know about the H5N1 virus:
Is a human pandemic inevitable?
Among birds and animals, H5N1 avian influenza is already a pandemic, or panzootic, with infections seen on every continent except Australia. To date, the virus has not evolved into a form that can spread easily from one person to another, and it may never do so.
As its name indicates, H5N1 has been a problem primarily in birds. But it has now spread to a wide range of species, from seabirds and small scavengers like foxes to large mammals, like bears and cows.
There have been sporadic infections among people since 1997, when an outbreak of cases occurred in Hong Kong. But most patients worldwide have been in close contact with infected animals and have generally not transmitted the virus to other people.
To become proficient at person-to-person transmission, H5N1 would have to undergo several additional mutations and change its shape. The strain isolated from the infected farmer in Texas carries one of those mutations, but that change has appeared before — in humans, foxes and seals, among others — without further consequences.
Human infections so far “fortunately are still all transmitted only once from one species to another,” said Vincent Munster, a virologist at the National Institute of Allergy and Infectious Diseases who has studied the mutations needed for H5N1 to adapt to the people.
History suggests that even if the virus changes enough to begin widespread transmission among people, it may have to give up something in return, Dr. Munster said. For example, when other influenza viruses adapted to humans, they lost much of their virulence, causing only mild symptoms.
How will we know if the virus spreads to people?
H5N1 is an influenza virus followed by extensive scientific networks that monitor influenza viruses around the world.
“We've been keeping an eye on this for years,” Dr. Daskalakis said.
These surveillance networks have tracked H5N1 even before its surge in birds and animals over the past two years. Now I'm on high alert. Scientists are looking for mutations that could make H5N1 more likely to infect people or resistant to vaccines and drugs available to fight it.
The World Health Organization, CDC and other global health organizations regularly share information and genetic sequences to track which flu strains are spreading where.
In the current outbreak, the Department of Agriculture shared the genetic sequences of infected cows with the CDC, which analyzes the sequences and ensures that stockpiled vaccines and drugs are still effective.
Do we have a vaccine for bird flu?
YES.
BARDA has enough vaccine building blocks – including adjuvants, substances that can increase the strength of a vaccine – to produce millions of doses in weeks. If necessary, mass production could also ramp up quickly, federal officials said.
The CDC already has two candidate viruses that can be used to make vaccines. As the virus changes, such as acquiring mutations that make it resistant to current vaccines and drugs, federal researchers could create new candidates.
Three pharmaceutical companies could be asked to produce avian flu vaccines, but those vaccines would be made on the same production lines used to produce seasonal flu vaccines. Before embarking on large-scale production, federal officials should consider the implications of disrupting seasonal production, said David Boucher, director of infectious disease preparedness and response at the Department of Health and Human Services.
Not all pharmaceutical companies use egg-based methods to produce vaccines, an important consideration because of the risk of avian flu outbreaks derailing the nation's egg supply. BARDA is also looking to add mRNA to the list of technologies that can be used to produce avian flu vaccines. (The Covid-19 vaccines produced by Pfizer and Moderna were based on this method.)
And the treatments?
At least four antiviral drugs are available to treat people who might get sick from bird flu, including the widely available generic drug oseltamivir, sometimes marketed as Tamiflu.
Unlike vaccines, which are stockpiled by the federal government, antiviral drugs are commercially available. Generic versions of oseltamivir are produced by many manufacturers around the world.
The federal government has a stockpile of tens of millions of doses of oseltamivir, Dr. Boucher said. The government is in close communication with manufacturers who could quickly ramp up production of oseltamivir, as it has done in the past during some bad flu seasons.
All these preparations are in place to deal with the worst-case scenario, but “we're not at that point yet,” Dr. Boucher said. “Our job here is to prepare for the worst should it come.”