Outbreaks of bird flu in dairy cows in several states, and even an infection in a farm worker in Texas, have raised fears that the virus may be the next infectious threat to humans.
The influenza virus, called H5N1, is highly pathogenic, meaning it is capable of causing serious illness and death. But while its spread among cattle is unexpected, people can get the virus only from close contact with infected animals, not from each other, federal officials said.
“It’s really about people being in environments where they might be in contact with cattle infected with this virus,” said Dr. Demetre Daskalakis, the 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. “Right now, our risk assessment hasn’t changed, but if it does, we’ll be quick and pretty transparent about that.”
Avian influenza is usually fatal in birds, but none of the infected cattle have died so far. The only symptom in the Texas patient was conjunctivitis, or pink eye, which has also been reported in people infected during other bird flu outbreaks.
The CDC and other agencies in the United States and elsewhere have been monitoring H5N1 for years to track its evolution. Federal agencies have stockpiled vaccines and drugs to be used in a possible bird flu outbreak.
“We are better prepared for a flu pandemic than perhaps any other outbreak that could happen, any other pathogen,” said Rick Bright, the chief executive of Bright Global Health, a consulting firm dedicated to improving responses to public health emergencies.
Led by Dr. Bright has been preparing for the flu at the Biomedical Advanced Research and Development Authority, or BARDA, the federal agency that supports research into vaccines and drugs for emergencies, for several years before he served as the agency’s director from 2016 to 2020. .
Here’s what you need to know about the H5N1 virus:
Is the human pandemic inevitable?
In birds and animals, H5N1 bird flu is now pandemic, or panzootic, with infections seen on every continent except Australia. So far, the virus has not evolved into a form that can easily spread from one person to another, and it may never do so.
As its name suggests, H5N1 has primarily been a problem in birds. But now it has spread to a wide range of species, from seabirds and small scavengers such as foxes to large mammals, such as bears and cows.
There have been sporadic infections in humans since 1997, when a cluster of cases appeared in Hong Kong. But most patients around the world have come into contact with infected animals, and they generally do not transmit the virus to other people.
To become adept at transmitting between humans, H5N1 had to acquire several additional mutations and change its shape. The strain isolated from the infected farmworker in Texas carries one of those mutations, but that mutation has appeared before — in humans, foxes and seals, among others — without further consequences.
Infections in humans today are “fortunately all still single-time cross-species transmission,” said Vincent Munster, a virologist at the National Institute of Allergy and Infectious Diseases who has studied mutations needed for H5N1 to adapt to humans.
History suggests that even if the virus mutates enough to initiate mass transmission between people, it may have to give something in return, Dr. Munster. For example, when other influenza viruses adapts to peoplehave lost most of their virulence, causing only mild symptoms.
How do we know if the virus is spreading between people?
H5N1 is an influenza virus followed by an extensive scientific network that tracks influenza viruses around the world.
“We have our eyes on it, and we’ve had our eyes on it for years,” said Dr. Daskalaki
These surveillance networks have been tracking H5N1 even before it has multiplied in birds and animals for the past two years. Now they are on high alert. Scientists are on the lookout for mutations that could make H5N1 more likely to infect humans or resistant to vaccines and drugs available to fight it.
The World Health Organization, the CDC and other global health organizations regularly share information and genetic sequences to track which flu strains are circulating and where.
In the current outbreak, the Department of Agriculture has shared genetic sequences from infected cows with the CDC, which is analyzing the sequences and making sure that stored vaccines and drugs are still effective.
Do we have a vaccine for bird flu?
Yes.
BARDA has enough building blocks for vaccines — including adjuvants, substances that can enhance a vaccine’s potency — to produce millions of doses in weeks. Mass production can also be ramped up quickly if needed, federal officials said.
The CDC already has two candidate viruses that could be used to make vaccines. As the virus evolves — developing mutations that make it resistant to current vaccines and drugs, for example — federal researchers can create new candidates.
Three pharmaceutical companies may be called upon to make bird flu vaccines, but those vaccines will be made on the same production lines used to make seasonal flu vaccines. Before embarking on large-scale manufacturing, federal officials need to consider the implications of disrupting seasonal production, said David Boucher, the director of infectious disease preparedness and response at the Department of Health and Human Services.
Pharmaceutical companies do not all use egg-based methods to produce vaccines, an important consideration given the potential for a bird flu outbreak to derail the nation’s egg supply. BARDA is also looking to add mRNA to the list of technologies that could be used to make bird flu vaccines. (Covid-19 vaccines made by Pfizer and Moderna rely on the method.)
What about treatments?
At least four antiviral drugs are available to treat people who may get bird flu, including the widely available generic drug oseltamivir, sometimes marketed as Tamiflu.
Unlike vaccines, which are stocked 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, said Dr. Boucher. The government is in close contact with manufacturers who can quickly scale up production of oseltamivir, as has happened in the past during several bad flu seasons.
All of these preparations are in place for a worst-case scenario, but “we’re not there yet,” said Dr. Boucher. “Our job here is to prepare for the worst and prepare for it should it come.”
