H5N1 infects second farm worker in California as feds bolster vaccine supply

California health officials yesterday announced the state’s second H5N1 avian flu infection in a dairy farm worker who had no known connection to its first case, as federal health officials announced new steps to boost the supply of H5N1 vaccines, if needed.

In related developments, federal officials today shared updates about the investigation into a recent Missouri H5N1 case with no clear exposure source and what other federal agencies are doing to manage the threat to people and animals.

California’s second patient also had conjunctivitis

Hours after California announced its first H5N1 case in a farm worker yesterday, officials announced a second similar case in a worker at a second farm impacted by recent outbreaks in cows. Both patients worked on farms in the Central Valley, where the virus has now been detected in 56 dairy farms since September.

The California Department of Public Health said, as in the first case, the second patient had mild symptoms, including conjunctivitis. Neither reported respiratory symptoms or was hospitalized.

The US Centers for Disease Control and Prevention (CDC) said it confirmed both cases as H5 avian flu, bringing the nation’s total to 16 cases since the first of the year. All but one—which involves a patient from Missouri—have been connected to contact with sick cows or poultry.

CDC scientists will conduct additional tests on the specimens from California’s patients, including genetic sequencing and attempting to isolate and grow the virus.

At a briefing today, Nirav Shah, MD, JD, the CDC’s principal deputy director, said the additional cases don’t change the CDC’s assessment that the risk to the general public is low, though more cases in people exposed to sick animals are expected.

He commended California officials for actively monitoring workers and quickly identifying and following up on people with symptoms. “This is public health in action,” Shah said.

Serology challenges in the Missouri investigation

At today’s briefing, Demetre Daskalakis, MD, MPH, who directs the CDC’s National Center for Immunization and Respiratory Diseases, said the agency’s scientists face a complex task in conducting serology tests to determine of any of the seven symptomatic contacts, six of them healthcare workers, of Missouri’s recent H5N1 patient had been infected with the virus.

He said H5 serology testing isn’t commercially available and that the process is more involved than clinical serologic testing. A sample of the live virus is needed to rule out a false-negative result. The work needs to be done in a biosafety level 3 lab, and because scientists couldn’t isolate the complete virus from Missouri’s confirmed patient, they had to reverse engineer one to match the Missouri virus. That step was completed on September 30.

He said scientists are moving at an accelerated pace and hope to have results by mid to late October.

Daskalakis also shared more details about Missouri’s investigation, including that the Missouri hospital instituted droplet precautions for the patient as soon as the respiratory virus panel showed a positive for influenza A. 

Missouri health officials conducted a traceback investigation, which identified 112 people at the hospital who likely had contact with the patient during the individual’s stay at the facility. Eighteen of them had higher-risk interactions before droplet precautions were introduced.

He said health systems are well prepared to detect another rare event, such as the one in Missouri, adding that all influenza A samples from Missouri are being subtyped, and no unusual signals have been seen from Missouri syndromic surveillance.

Feds double doses for national stockpile

At today’s briefing, David Boucher, PhD, director of infectious disease preparedness and response at the US Department of Health and Human Services’ (HHS’s)Administration for Strategic Preparedness and Response (ASPR), said the Biomedical Advanced Research and Development Authority (BARDA) has given $72 million in new awards to three vaccine companies to produce H5N1 vaccine. The awards cover more fill-and-finish activities, the production of additional bulk antigen, and maintenance of vaccine seed stocks.

The companies include CSL Seqirus, which makes a cell-based vaccine, and Sanofi and GSK, which make egg-based vaccine. 

Boucher said the overall H5N1 vaccine strategy, which includes mRNA vaccine development, is designed to pivot to new threats while leaning into other areas. Currently, H5N1 vaccination isn’t recommended for any group. 

The new manufacturing agreements will double the amount of finished H5 vaccine in the strategic national stockpile to just over 10 million doses by the end of the first quarter of 2025, he said.

On October 10, the Food and Drug Administration (FDA) vaccine advisory group will meet, partly to discuss the composition of H5 vaccines.

Bulk milk sampling in California

At today’s briefing, Eric Deeble, DVM, acting senior advisor for the US Department of Agriculture’s (USDA’s) H5N1 response, said bulk milk sampling has played a role in identifying all of California’s 56 H5N1 outbreaks so far.

He said that though the B3.13 genotype had been confirmed in the California outbreaks, state officials are still investigating how the virus is spreading among the state’s Central Valley dairy farms. California officials had already requested a USDA epidemiologic strike team, which will be increased from three to five members.

In California, agriculture officials are conducting weekly bulk milk samples at farms in a 10- kilometer (6.2-mile) radius around outbreak locations, he said. The strategy seems to have worked in Colorado, which has seen a dramatic reduction in outbreaks, even in the absence of a vaccine.

In other developments on the animal health side, Deeble said the USDA today released an H5N1  research agenda, which is part of broader H5N1 research priorities unveiled today by the HHS.