New pandemic risk from avian influenza virus

Scientists are increasingly concerned that gaps in bird flu surveillance could leave the world "several steps behind" a new pandemic.

Researchers have been tracking the new strain of H5N1 influenza in migratory birds since 2020, but they say the virus's current spread to 129 dairy herds across 12 states signals significant changes that could bring the virus closer to a future of human transmission.

'It's almost like a slow-moving pandemic. Right now, the threat is pretty low, but that can change in a split second, similar to Covid-19 ,' said Scott Hensley, a professor of microbiology at the University of Pennsylvania.

For example, federal monitoring of dairy cattle in the United States is currently limited to testing herds before they are transported across administrative borders. Testing is also inconsistent across regions. Screening of people who come into contact with livestock is limited, officials and pandemic experts say.

"We need to determine which farms have positive cases of influenza, how many cases, how widespread the virus is, how long a cow has been sick, what the exact transmission route is," said Ron Fouchier, a virologist at the Erasmus Medical Center in Rotterdam.

Similarly, Dr. Jeanne Marrazzo, director of the US National Institute of Allergy and Infectious Diseases, said clinical surveillance for the virus has been 'very, very limited .' She said the US Centers for Disease Control and Prevention's screening network has been 'quite passive,' noting that the US Department of Agriculture has been proactive in testing cows but has not publicly disclosed which farms have been affected. Some experts say that animal and human health agencies have responded differently to the situation, which could hamper the overall response.

Free-range chickens at Hilliker's Ranch Fresh Eggs, California, USA, April 2022. (Photo: Reuters).

In fact, some pandemics, including Covid-19, have come with little warning. In the last influenza pandemic (H1N1 in 2009), the virus initially circulated in animal populations for only a few years. This is similar to the current H5N1 pattern.

The United States has reported three positive cases of H5N1 since late March. The patients had contact with infected cattle and had mild symptoms. Mexico reported a separate case of a strain of H5 never before seen in humans. The patient had no contact with animals. Other isolated cases have emerged in India, China and Australia, caused by different strains.

The World Health Organization (WHO) says the risk of H5N1 infection in humans remains low, with no evidence of community transmission. There is a vaccine to prevent the disease (though limited supplies) and the drug Tamiflu to treat it. Many pharmaceutical companies have the capacity to produce large-scale influenza testing kits, treatments and vaccines if needed, said Wenqing Zhang, head of the WHO's influenza response unit.

The risk is high enough that countries should prepare for a human outbreak of avian influenza, said Richard Hatchett, executive director of the Coalition for Epidemic Preparedness Innovations (CEPI). The group has moved early on developing a Covid-19 vaccine and is in talks with partners to develop an H5N1 vaccine. CEPI aims to create a library of prototype vaccines for pathogens with pandemic potential, allowing pharmaceutical companies to begin large-scale production and distribution of the necessary vaccines within 100 days of an outbreak.

Countries prepare

Several countries are taking the first steps to protect their people from H5N1. The United States and Europe have purchased 'pandemic' vaccines that can be used in high-risk groups, including farm workers and laboratory professionals. Finland was the first country to vaccinate against bird flu.

But expanding vaccination campaigns is complicated. Manufacturers of 'pandemic' vaccines still have to produce seasonal flu vaccines. But they can't handle both at the same time. Most flu vaccines are made using viruses grown in eggs, which take six months to develop.

The US is negotiating with Moderna to use mRNA technology to help prepare a vaccine to prevent the pandemic more quickly.

All experts acknowledge the need to act quickly to contain the threat, but not overreact and cause public panic.

"We want to be cautious, but not give the public a sense of impending doom," said Wendy Barclay, a virologist at Imperial College London who advises the UK's Health Security Agency on bird flu.