WHO’s top scientist learned a hard lesson about H5N1 two decades ago: Stopping it takes more than biology

Jeremy Farrar, now the World Health Organization’s chief scientist, was working in Vietnam 20 years ago when the H5N1 virus started to spread across Asia — at that point in poultry. He recalls there was a reluctance among farmers to cull their chickens because they weren’t being compensated for them. Movement of infected birds to evade culling only served to disseminate the virus, which in the years since has spread to all continents except Australia.

It’s important to keep that experience in mind, he told STAT Monday, as the H5N1 bird flu virus now spreads among dairy cattle in the U.S. Farrar stressed that the social context is key in responding to disease threats like H5N1, noting that a similar reluctance among dairy farmers to report outbreaks or allow testing of their workers is adding to the challenges in assessing how much transmission is occurring and the risk it poses to people.

“You can’t just take the virus and the biological surveillance and divorce it from the environment and the social construct that it’s happening in,” Farrar said in an interview from WHO headquarters in Geneva. “That’s the reality.”

Though it is believed the virus has been spreading in dairy cow herds for months, to date the U.S. Department of Agriculture has confirmed only 36 infected herds in nine states. There have been no new outbreaks announced in the week since a federal rule went into effect requiring testing of a portion of the cows in a cattle shipment that is destined to cross state lines, if the cows are lactating. (The infections to date have been detected in lactating cows.)

On the human health side, there have been multiple anecdotal reports of farm workers who’ve been exposed to infected cattle suffering from conjunctivitis and other mild symptoms. But Todd Davis, acting chief of the virology, surveillance and diagnosis branch of the Centers for Disease Control and Prevention’s influenza division, told a WHO webinar on Monday that only about 30 people have been tested since the outbreak was first detected in late March. There has been one confirmed infection, in a farm worker from Texas who had conjunctivitis.

Both the USDA and the CDC have acknowledged that many farmers have been unwilling to allow testing of their animals or to permit public health officials to speak with or conduct testing on their workers. The industry is known to employ migrant and even sometimes undocumented workers, which perhaps explains the unwillingness of those workers to comply with public health efforts to study what is going on in these outbreaks.

“I know many people within that industry in the United States and other parts of the world are workers paid in a certain way, hourly or daily. They may be reluctant to report illnesses. It’s an epidemic of a virus, but the social context it’s happening in is just critical,” Farrar said.

Ideally, public health workers would have drawn blood samples from the Texas worker who tested positive for H5N1 and from people he worked with and lived with, to look for undetected cases that could suggest onward transmission of the virus. But he and the people he lived with refused to allow blood samples to be taken.

While he believes the risk of a human flu pandemic triggered by the H5N1 virus is low, should it happen, the social context will also be crucial, Farrar continued. The mental toll of the taxing Covid-19 pandemic hangs over the public, health care workers, public health agencies, and governments. Getting people to again buy into measures that might slow spread, such as social distancing or school closures, would likely be tough, he said.

“The hangover is absolutely true across all societies, I think,” Farrar said. “Public health agencies but also health care workers around the world are shattered. … It’s a global phenomena and the world’s willingness to either have vaccines, mRNA, or otherwise, and have any school closures, masks, whatever interventions you may talk about, would not be the same as they were back in 2020.”

All the more reason, Farrar suggested, to take the actions needed to ensure the spread of bird flu in cows does not trigger a worse crisis. “That makes the case that we better do what we can to avoid an event happening because I think the response would understandably be very different.”