The Centers for Disease Control and Prevention announced Tuesday that it is funding a $5 million program to vaccinate livestock industry workers against seasonal flu in a bid to reduce the pandemic risk posed by the ongoing H5N1 bird flu outbreak in cattle.
The voluntary program, which will be administered by state and local public health workers, is aimed at getting seasonal flu shots into as many people as possible who are working in proximity to animals — poultry, cows, or other livestock — that could be infected with H5N1. Nirav Shah, the CDC’s principal deputy director, said there are an estimated 200,000 people officially working in this sector nationwide, though he acknowledged that number doesn’t encompass all people working with these animals.
H5N1 could evolve to become a pandemic flu strain one of two ways, by gradually acquiring mutations that give it the ability to easily infect and spread among people, or by swapping genetic material with other flu viruses, such as H3N2 or H1N1, the influenza A viruses that circulate and cause illness during the flu season. That gene swapping, a process called reassortment, can occur when an animal or a person is infected at the same time with two or more flu A viruses.
The rationale for the CDC program is to lower the risk that farmworkers will be infected with human flu strains during the coming flu season and, if they go to work sick, transmit human flu viruses to cows or other mammals already infected with H5N1, or themselves become co-infected with the bird flu virus.
“In theory, reassortment could lead to a new influenza virus that could pose a significant public health concern. A virus that has the transmissibility of seasonal influenza and the severity of H5N1,” Shah, the CDC’s principal deputy director, said during a press conference featuring the CDC and officials of the U.S. Department of Agriculture. “We want to do everything we can to reduce the risk that the virus may change because of co-infection and reassortment.”
For the time being, though, “everything” stops short of offering these same workers H5N1 vaccine from the U.S. National Pre-pandemic Influenza Vaccine Stockpile. Finland is vaccinating mink farm workers against H5N1, which has caused outbreaks in these animals. But the U.S. government has said at this point it doesn’t see a value in following suit.
“Given the low rates of [human H5N1] infection overall, the mild symptoms, the lack of person-to-person [transmission], I don’t think the question is: Why not do it? I think the question is: Why do it?” Shah said.
Shah said there are ongoing discussions among U.S. officials about whether to offer H5N1 vaccine to farmworkers, but “for right now, the seasonal flu shot is the right tool for the job.”
The CDC will spend up to $2 million on the flu shots, with the remaining $3 million going to finance on-the-ground efforts to get the vaccine to farmworkers, Shah said. Implementation will look different from location to location, he noted, and may involve bringing vaccine doses to farms, or setting up vaccination booths at public events that are frequented by farmworkers.
Since the outbreak of bird flu in cows was first recognized in late March, 13 workers have been diagnosed with H5N1. All the cases to date have been mild. Four of the cases were farmworkers infected while working with dairy cattle; the other nine were people who were infected while culling chickens when the virus from cows spilled over into two large poultry operations in Colorado.
Since the outbreak was first recognized, the USDA has confirmed infections in 172 herds in 13 states.
Eric Deeble, USDA’s point person for H5N1 in dairy cows, said the department continues to believe the outbreak can be contained. “Given that we have seen a real increase in awareness of producers and an increase in biosecurity, we believe that we can arrest the spread of this disease and ultimately eradicate it in dairy cattle on the farms,” he said.
Another USDA official indicated that the department has been studying viruses from the outbreak on an ongoing basis and is not seeing evidence that the virus has been evolving in cows, calling it “very stable up to this point.”