There is not enough testing for bird flu among people and animals in the US, says Dr Nirav Shah, principal deputy director of the US Centers for Disease Control and Prevention (CDC) – but he is wary of pushing the issue and damaging fragile trust among farm workers and owners.
“We would like to be doing more tests,” Shah said. “We’d like to be testing particularly not just symptomatic workers, but anyone on a farm who is exposed.”
But, Shah said, “right now we want to be in a role where we’re building trust with farms and farm workers.”
For the general public, the risk is still low, the CDC says. But the risks are elevated for agricultural workers in close contact with animals – and potentially the people around them.
The CDC is “preparing for the possibility” that the virus could evolve to spread more easily among people, according to a report published on Wednesday.
Shah encouraged the use of personal protective equipment, but stopped short at promising shots for farm workers, who are now the most at risk for getting and spreading H5N1, a highly pathogenic bird flu.
US officials announced last week that a third person tested positive – a farm worker in Michigan who worked closely with sick cows.
Unlike the previous two cases, where conjunctivitis (or “pink eye”) was the only symptom, this patient experienced respiratory symptoms typical for the flu – a cough, congestion, sore throat and watery eyes.
Shah was quick to point out these symptoms don’t mean the virus is changing. Symptoms like these have been common in the 888 people who have tested positive for H5N1 since 2003.
“This virus, like many viruses, can present in more than one way. And for that reason, we should remain alert, not alarmed,” he said.
But having respiratory symptoms means the individual has more opportunities to pass the virus on to other people, he said, making monitoring and testing even more important than before.
Yet only 44 people have been tested in 2024, according to the CDC.
While officials believe there are probably cases flying under the radar due to the lack of testing, they are closely analyzing data from influenza monitoring systems, and no red flags have been observed yet. “We have not detected any differences in markers, like emergency room visits, in areas with affected herds compared to areas without affected herds,” Shah said.
“Our influenza infrastructure is strong, and it’s notable to discuss the ways in which it differs from our Covid infrastructure,” he said. There are tests available throughout the country, there is a good vaccine candidate for this strain currently being manufactured and the virus monitoring system is already well established.
“That said, we’d love to be doing more,” he continued.
Some states are now testing the blood of dairy farm workers to see how many people have antibodies against H5N1, which would give scientists a better idea of how much the virus is circulating. “We’ve done these studies in poultry [workers] over the years. We’d like to replicate them now in dairy farm workers,” Shah said.
Officials have also expanded the ways people can be tested for H5N1, including eye swabs in test kits to check for conjunctivitis. These eye swabs may now be tested at local labs instead of being sent to the CDC.
“Now we don’t wait until these tests are confirmed [by the CDC] before public health action is taken,” Shah said.
H5N1 continues spreading among farms, including poultry operations, with 4.2 million egg-laying chickens killed on a farm in Iowa after the virus was detected.
In Idaho, alpacas tested positive on 16 May after an outbreak among poultry on the same farm – a sign that the highly pathogenic flu may be spreading from cows to poultry to other livestock, potentially accumulating mutations.
The second person to test positive in the US bird flu outbreak this year showed a mutation that may make the virus spread more among mammals, genetic sequencing revealed.
No genomic analysis of the third case has been announced yet.
While the US Department of Agriculture announced another $824m in funding to protect livestock last week, health officials have not announced additional funds for this outbreak beyond the $101m for the CDC and the Food and Drug Administration (USDA) announced in May.
Part of the USDA funding has included up to $2,000 a month to farms for providing personal protective equipment, or PPE, such as N95 respirators, face shields and goggles.
The CDC has asked states to distribute personal protective equipment to farm workers from their existing supplies as well as from the strategic national stockpile.
“Thankfully, there’s quite a lot of PPE available out there. Now the task is just connecting those who have PPE with those who need it,” Shah said.
But officials are mindful of the inherent difficulties of wearing, for instance, an N95 mask while working on a farm – from the wet nature of dairy farming to summer heat.
“We want our workers to be maximally protected, while at the same time not compromising their health and safety because they’re overheating,” Shah said.
US officials have ordered 4.8m doses of an H5N1 vaccine they say seems well matched to this strain. It takes several months to create flu vaccines, and new formulations like this then go through regulatory processes for authorization or approval.
Officials have shied away from saying who might be prioritized for the vaccines.
“There is not right now a recommendation to vaccinate farm workers,” Shah said. “Of course, it’s under discussion. As scientists, as scientific organizations, we are always discussing what might be coming next and evaluating the pros and cons of that.”
Shah highlighted the importance of community trust in public health, especially since H5N1 is an emerging disease in livestock. Poultry producers, for example, have built up relationships with officials and regulators over decades of bird flu outbreaks.
Trust is “the most important tool that you have in your toolbox in an outbreak setting”, Shah said.
“When H5 became a phenomenon in the poultry industry, it was not overnight that poultry farm owners, operators, as well as workers were ready to work with public health entities – that relationship took time to develop,” Shah said. “The same thing is under way here.”
That means being clear about what testing does and doesn’t entail, and assuring the privacy of workers, he said.
“It’s not something that happens overnight, but we have made progress with farms and farm owners. We want to continue that, rather than trying to overplay our hand and shatter the trust that we’ve created so far.”
