A dairy worker in Nevada has been confirmed to be infected by a new bird flu strain found to be spreading among cows in the state last week.
That strain of the H5N1 bird flu virus, called D1.1 by scientists, is different from a previous variant called B3.13 which had infected at least 40 dairy workers in the U.S. to date.
D1.1 was also behind a fatal case in Louisiana in a person who was hospitalized last year, raising concerns that the strain might lead to more severe disease in humans. The Centers for Disease Control and Prevention says 14 other cases last year have also been linked to D1.1 from birds, which did not result in hospitalization.
B3.13 has led to only symptoms of conjunctivitis — or pink eye — in many cases and research suggests it is less severe for humans than other bird flu strains.
So far, health authorities in Nevada say the dairy worker, who tested positive after working with sick cows in the state’s Churchill County, had only pink eye as their symptom and is now recovering.
“There is currently no evidence of person to person spread of this virus. Close contacts of the infected person and other workers exposed at the farm are being contacted and monitored for symptoms and are being offered personal protective equipment (PPE), testing and antiviral medication,” the Central Nevada Health District said in a statement.
Owen Truesdell, a spokesperson for the health district, said there is currently no evidence of other dairy workers showing symptoms.
“Please note that this is an evolving situation and we will continue to communicate with reporters and the public when relevant new information is learned,” Truesdell said in an email.
Health officials have said for months that while the spread of the virus in animals warrants stepping up precautions for workers dealing with sick cows and birds, the risk to the general public remains low.
“This case involving cow-to-human spread of H5 in a person with higher-risk occupational exposure does not change CDC’s risk assessment, which remains low for the public but is higher for people with occupational or recreational exposures,” a CDC spokesperson said in a statement.
Virologists have said that multiple key mutations would need to change in the virus before it could easily spread between humans, beyond the occasional dead-end spillovers seen so far from animals into humans.
An analysis published by the U.S. Department of Agriculture on Friday found that one “mammalian adaptation” had been found in the virus from the D1.1-infected cows in Nevada last month, but said there was “no evidence of onward transmission among humans.”
Will vaccines work for D1.1?
While the seasonal flu vaccine is not designed to boost protection against H5N1, there are different kinds of vaccines that health authorities have prepared for a potential bird flu pandemic.
Health authorities routinely test those pandemic vaccines against the bird flu virus to see if new strains have evolved to escape the protection from those shots.
Previous testing by the CDC with D1.1 strains spreading in wild birds have found that the pandemic vaccines stockpiled by the U.S. government should still offer protection, two health officials told CBS News.
Dr. Richard Webby, head of a World Health Organization influenza collaborating center at St. Jude Children’s Research Hospital, said those tests were done using antibodies after infection.
“It is anticipated that vaccination will induce an even better response,” said Webby in an email.
Why aren’t we vaccinating for bird flu?
Under the Biden administration last year, the Administration for Strategic Preparedness and Response moved to prepare enough vials to vaccinate 2.4 million people if needed — but so far those doses have not been distributed for use.
Officials said at the time that there was not yet a need to roll out the immunizations, citing the largely mild symptoms in infected workers and lack of human-to-human spread.
Virtually all U.S. human cases of bird flu have been linked to direct contact with sick animals, often during intensive exposures like caring directly for sick animals or culling large flocks of infected birds. That includes the person who died in the Louisiana case, who had direct contact with sick birds.
But there have also been three cases over the past year with an “unknown” exposure, where investigators were unable to track down a likely explanation for how people got sick.
More clues to one of those bird flu cold cases could come this month, when the CDC is expected to have results from a study looking at blood samples that might reveal missed infections among contacts of a child sickened in San Francisco.
“No additional cases have been identified and there remains no evidence of human-to-human transmission,” a spokesperson for San Francisco’s Department of Public Health said on Jan. 24.
