A recent mammal H5N1 avian flu strain and an H5N1 virus strain from an infected Texas dairy worker showed low but increased ability to transmit by air compared to older H5N1 strains, according to a ferret study published yesterday by a research team based at Erasmus University Medical Center in the Netherlands.

To assess the public health risk of the newer H5N1 viruses, the team examined virus shedding in the air by examining experimentally infected ferrets. The animals were placed in cages connected to aerosol samplers that captured infectious virus expelled in the air. The group published its findings in Nature Microbiology.
With groups of four ferrets, scientists tested six different viruses to assess differences in airborne shedding, which included 2009 H1N1 seasonal flu, a wild-type zoonotic Indonesian H5N1 virus from 2005 and a modified version of the virus that was earlier found to be transmissible by the air among ferrets, a 2022 H5N1 virus from a European polecat, a 2024 H5N1 virus from a Texas dairy worker, and a 2024 H5N1 virus from an Ohio dairy cow.

Results were similar to transmission studies

The researchers found that the 2009 H1N1 virus was efficiently shed by the ferrets in the air, but air sampling didn't detect any older wild-type or recent bovine virus. Meanwhile, they observed shedding for one of four ferrets infected with the 2022 polecat strain and the 2024 virus isolated from the dairy workers.

They said the shedding data resembled results from ferret-to-ferret transmission studies and that the lack of shedding in the air rather than the absence of mammalian adaptation mutations may explain the absence of transmission of the older H5N1 viruses.

"Given the ongoing epizootic in cattle and the high risk of exposure for farm and dairy workers and domestic and wild mammals to infected cows and contaminated milk, it is crucial for effective outbreak control and public health safety to understand how this virus spreads among cattle, its potential for mammalian adaptation and its capacity for airborne transmission," the authors concluded.

A study in infants in primary care settings in Spain finds an overall effectiveness of 76% for the monoclonal antibody nirsevimab in preventing medically attended respiratory syncytial virus (RSV) respiratory tract infections. The study is published in Pediatrics. 

The study looked at 160 infants 10 months and younger who received the antibody during the 2023–2024 RSV season.  All infants were born after April 1, 2023, and received nirsevimab either at birth in hospitals or during a catch-up program before the RSV season started. 

The main outcome was medically attended lower respiratory tract infection (LRTI) caused by RSV. 

Catch-up reduces load in primary care offices 

Overall, 141 infants (88%) received nirsevimab, with 29 (21% of the sample) administered in-hospital during the RSV season, and 112 (79%) through the catch-up program, the authors said. Sixty-seven percent of infant were aged at least 3 months, and most were boys (64%). 

RSV was detected in 44 infants (27.5%) included in the study. Within the catch-up group, 37 (28.9%) were positive for RSV. 

The overall effectiveness was 75.8% (95% credible interval [CI], 40.4 to 92.7), and 80.2% (95% CI, 44.3 to 95.4) in infants belonging to the catch-up group.

This study demonstrates the effectiveness of nirsevimab in preventing medically attended RSV-LRTI in infants aged younger than 10 months in a large primary care network in Spain, both overall and for the catch-up group.

"This study demonstrates the effectiveness of nirsevimab in preventing medically attended RSV-LRTI in infants aged younger than 10 months in a large primary care network in Spain, both overall and for the catch-up group,” the authors concluded. The authors also said catch-up nirsevimab administration is a powerful tool for reducing primary care burden during RSV season.  

The UK Health Security Agency (HSA) today announced a contract with CSL Seqirus to buy more than 5 million doses of human H5 avian flu vaccine to prepare for a potential influenza pandemic. 

In a statement, the HSA said the vaccine will be based on a current H5 strain and is part of a longer-term plans to ensure access to vaccines for a wider range of pathogens that have pandemic potential.

Meera Chand, PhD, the HAS's emerging infection lead, said, "Early access to vaccines saves lives. Adding H5 vaccines to the interventions already available to us will help us to be ready for a wider range of threats."

The agency said the vaccine would be used only if the virus starts spreading among people. If needed, the H5 vaccine could be used while a pandemic-specific vaccine is developed and produced. The UK government already has an advance purchase agreement in place for pandemic vaccines if and when they are needed.

Other countries and regions are also stockpiling H5 vaccine, including the United States, the European Union, and Japan.

More H5N1 confirmed in US dairy herds and poultry

In other H5N1 developments, the US Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) today confirmed 6 more outbreaks in dairy cattle, all in California. The new outbreaks lift California's total since late August to 481 and the national total to 695 from 15 states.

Also, APHIS confirmed two more outbreaks in poultry, one involving a flock of 80 birds in North Dakota's Bottineau County and the other a backyard location in Oregon's Union County that has 30 birds.

The odds of receiving first-line (FL) antibiotic therapy at pediatric urgent care centers (PUCs) were lower in White children and those with commercial insurance than other groups, according to a study today in Infection Control & Hospital Epidemiology.

For the study, researchers with the REDUCE (Reducing Differences in Urgent Care Encounters—Antibiotic Choice) Collaborative evaluated use of guideline-recommended FL antibiotics for acute respiratory infections (ARIs) in children 6 to 18 months of age at US PUCs from April 2022 to April 2023. ARIs included viral respiratory infections, otitis media (ear infection) with effusion (OME), acute otitis media (AOM), pharyngitis, community-acquired pneumonia (CAP), and sinusitis. The aim of the study was to determine whether differences exist in antibiotic prescribing for ARIs in relation to race and ethnicity, insurance, and language. 

Small but potentially significant differences

The analysis included 396,340 ARI encounters at 28 PUCs. The median age of the cohort was 51 months, and 351% of the children were White, 25% were Hispanic, 9.2% Black, and 6.4% Asian. Race and ethnicity were unknown in 20.7%. Most children (55.8%) had commercial insurance.

Among all encounters, 351,930 (88.8%) received FL therapy (98% for viral respiratory infections, 85.4% for AOM, 96.0% for streptococcal pharyngitis, 83.6% for sinusitis). OME and CAP had the lowest rates of FL therapy (49.9% and 60.7%, respectively). Adjusted odds of receiving FL therapy were higher in Black (adjusted odds ratio [aOR] 1.53; 95% confidence interval [CI], 1.47 to 1.59), Asian (aOR 1.46; 95% CI, 1.40 to 1.53), and Hispanic children (aOR 1.37; 95% CI, 1.33 to 1.41) than in White children. 

Additionally, the odds of receiving FL therapy were higher in children with Medicaid/Medicare (aOR 1.21; 95% CI, 1.18 to 1.24) and self-pay (aOR 1.18; 95% CI, 1.1 to 1.27) than in commercially insured children.

"While the differences reported in our study are relatively small, they are potentially clinically significant and are persistent across centers and diagnoses," the study authors wrote. "Understanding the causative factors contributing to the differences in antibiotic prescribing behaviors will be helpful in developing strategies for equitable antibiotic stewardship."

A population-wide cohort study in Ontario found that more than 15% of residents colonized with an antimicrobial-resistant (AMR) pathogen went on to develop an infection with the same pathogen, researchers reported yesterday in Open Forum Infectious Diseases.

Using population-level health administrative data, a team led by researchers with the University of Toronto investigated the risk of infection among a cohort of residents of Ontario who had a positive surveillance test for a resistant pathogen from January 1, 2017, to December 31, 2021. The specific organisms of interest included methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), extended-spectrum beta-lactamase–producing Enterobacterales (ESBL), and carbapenemase-producing Enterobacterales (CPE). The researchers also examined the effects of age, sex, and healthcare setting of colonization detection on subsequent infection risk.

Among the 69,998 people with a positive surveillance test during the study period, 15.6% subsequently developed a sterile or non-sterile site infection, within a median of 57 days. Infection rates varied between organisms: 18.3% for MRSA within a median of 57 days, 2.8% for VRE within a median of 37 days, 21.5% for ESBL within a median of 71 days, and 20.3% for CPE within a median of 10 days. More than half of all infections occurred within 90 days.

The association of age and sex with infection risk was variable, but a positive surveillance test detected in a hospital was universally associated across all resistant organisms with increased infection risk after colonization compared with the community setting.

Higher risk than previously found

The study authors say the observed rate of infection after colonization is higher than has been found in previous studies, which have been limited by small sample size, single-care settings, and exclusive focus on high-risk patients or settings.

"Colonization with an AMR pathogen has variable infection risk depending on the specific pathogen, but the overall risk is likely higher than what has previously been reported for most organisms, highlighting the importance of detecting colonization from both an infection control and empiric antibiotic selection perspective," they wrote.

They suggest future studies could use the same cohort to examine clinical predictors of progression from colonization to infection.