Bird flu outbreaks among dairy cows in multiple states and at least one infection in a farm worker in Texas have raised fears that the virus could be the next infectious threat to humans.
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 only catch the virus through close contact with infected animals, not from each other, federal officials said.
“It’s really about people who are in environments where they might interact with cattle that are infected with this virus,” said Dr. Demetre Daskalakis, director of the Centers for Disease Control and Prevention’s National Center for Immunization and Respiratory Diseases. the diseases.
“The risk to most others is very low,” he added. “Right now our risk assessment hasn’t changed, but if it does, we’ll be pretty quick and pretty transparent about it.”
Bird flu is often fatal in birds, but so far none of the infected cows have died. 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 tracked H5N1 for years to monitor its development. Federal agencies have stockpiled vaccines and drugs to be used in a possible bird flu outbreak.
“We’re more prepared for an influenza pandemic than probably any other outbreak that could occur, any other pathogen,” said Rick Bright, CEO of Bright Global Health, a consulting company that focuses on improving of public health emergency responses.
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 the agency’s director 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 now a pandemic or panzootic, with infections occurring on every continent except Australia. To date, 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 been a problem primarily in birds. But now it has 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 human infections since 1997, when a cluster of cases emerged in Hong Kong. But most patients around the world were in very close contact with infected animals and generally did not transmit the virus to other people.
To become adept at human-to-human transmission, H5N1 will need to pick up a few additional mutations and change shape. The strain that was isolated from the infected farm worker in Texas carries one of these mutations, but this change has occurred before—in humans, foxes, and seals, among others—without further consequences.
Human infections so far “fortunately have all still been one-time cross-species transmissions,” said Vincent Munster, a virologist at the National Institute of Allergy and Infectious Diseases who has studied the mutations H5N1 needs to adapt to humans.
History suggests that even if the virus changes enough to start spreading widely among humans, it may have to give up something in return, Dr. Munster said. For example, when other flu viruses adapted to humans, they lost much of their virulence, causing only mild symptoms.
How will we know if the virus is spreading among people?
H5N1 is an influenza virus that is followed by extensive scientific networks that track influenza viruses around the world.
“We’ve had our eye on this and have had our eye on it for years,” Dr. Daskalakis said.
These surveillance networks tracked H5N1 even before its rise in birds and animals over the past two years. Now they are on high alert. Scientists are watching for mutations that could make H5N1 more likely to infect humans or become resistant to available vaccines and countermeasures.
The World Health Organization, the CDC and other global health organizations routinely share information and genetic sequences to monitor which flu strains are spreading and where.
In the current outbreak, the USDA has shared genetic sequences from infected cows with the CDC, which analyzes the sequences and ensures that stockpiled vaccines and drugs are still effective.
Do we have a bird flu vaccine?
Yes
BARDA has enough vaccine building blocks — including adjuvants, substances that can improve a vaccine’s potency — to make millions of doses in weeks. Mass production also could 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 changes — acquiring mutations that make it resistant to current vaccines and drugs, for example — federal researchers can create newer candidates.
Three pharmaceutical companies may be called upon to make bird flu vaccines, but those vaccines will be produced on the same production lines that are used to make seasonal flu vaccines. Before starting large-scale production, federal officials will need to consider the consequences of disrupting seasonal production, said David Boucher, director of infectious diseases at the Federal Strategic Preparedness and Response Administration.
Not all pharmaceutical companies use egg-based methods for vaccine production, an important consideration because of the potential for bird flu outbreaks to disrupt 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. (Covid-19 vaccines made by Pfizer and Moderna relied 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 sold as Tamiflu.
Unlike vaccines, which are stored by the federal government, antiviral drugs are available commercially. Generic versions of oseltamivir are produced by many manufacturers worldwide.
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 of these preparations are in place for a worst-case scenario, but “we’re not there yet,” Dr. Boucher said. “Our job here is to prepare for the worst and be ready for it in case it does come.”
