Avian flu and seasonal flu are colliding in California

By Rachel Bluth, David Lim, Marcia Brown | 10/17/2024 11:58 AM EDT

Officials are racing to vaccinate dairy workers against the seasonal flu to prevent the two viruses from combining.

A line of Holstein dairy cows feed through a fence at a dairy farm.

The Food and Drug Administration plans to beef up milk testing later this month, deploying a separate study across participating states to discern how far the virus has spread. Charlie Litchfield/AP

SACRAMENTO, California — Health officials across the U.S. are working to prevent a potentially dangerous combination virus as avian flu rips through one of the nation’s largest milk-producing regions during the height of flu season.

Public health experts have long warned that avian flu poses a significant pandemic threat to humans, and the number of infections among dairy workers in California continues to grow. The timing of the outbreak will soon collide with the seasonal flu, complicating efforts to track bird flu and raising the risk that the two viruses could mix, potentially creating a virulent combo that could spread beyond dairy workers to the rest of the population.

Despite what California officials say is a proactive approach, public health experts outside the state say too little is being done to track and respond to avian flu, which has spread to 105 dairy farms since the virus was first found here in August. The stakes are high: Approximately half of documented human H5N1 avian flu cases in the past two decades were deadly, according to the World Health Organization.

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“It will mutate to become increasingly optimal in humans as soon as it gains any foot in the door for human-to-human transmission,” said Michael Mina, chief science officer at digital health company eMed. “How far that goes and how fast it means the virus starts to transmit … is almost entirely unknown right now.”

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