UNITED KINGDOM —Global experts on influenza have met this week to discuss the potential risk to humans posed by the H5N1 avian flu virus, which has caused a record number of bird deaths worldwide in recent months.

During the meeting, which takes place twice a year, the group of scientists, regulators, and vaccine manufacturers discussed the strain of seasonal flu to include in the vaccine for the upcoming winter season, as well as the risk of animal viruses spilling over to humans and causing a pandemic.

The H5N1 clade was a key topic of discussion, according to the World Health Organization (WHO) and global flu experts.

While there have been very few human cases, reports of mass deaths in infected mammals from seals to bears and potential mammal-to-mammal transmission on a Spanish mink farm last year have raised concern.

The WHO currently assesses the threat to humans as low, but experts discussed potential vaccine development during the meeting.

WHO-affiliated labs already hold two flu virus strains that are closely related to the circulating H5N1 virus, which could be used by vaccine manufacturers to create a human vaccine if needed.

However, getting enough vaccines developed quickly would still remain a challenge in a pandemic situation, the experts said.

A number of companies that produce seasonal flu vaccines can also make pandemic flu vaccines. For example, GSK and CSL Seqirus are already working with the United States Biomedical Advanced Research and Development Authority (BARDA) to test shots based on one of the closely-related strains.

The world is currently experiencing a global outbreak of Highly Pathogenic Avian Influenza A(H5N1), also known as bird flu.

This strain has infected poultry and wild birds worldwide, with the current outbreak being the worst in US history. More than 60 million birds have died or have been culled due to exposure to infected birds.

H5N1 was first detected in China in 1996 in domestic waterfowl, and the first human cases emerged during a poultry outbreak in China and Hong Kong in 1997.

Since then, new versions of the virus have emerged globally in wild and poultry populations, until the H5N1 virus belonging to clade became the dominant virus circulating at the end of 2021.

While H5N1 mainly affects avian species, spillover into mammalian species has been reported.

In January 2023, grizzly bears in Montana tested positive for avian influenza, and the virus has been found in more than a dozen mammal species in the past year.

Human infection with H5N1 is rare and mainly affects those in close contact with birds, such as poultry farm workers or those with smaller flocks at home.

Since 2003, there have been 868 cases of human infection reported, with a high fatality rate of 53%.

Since the 1918 flu pandemic, there have been three flu pandemics – H2N2 in 1956-7, H3N2 in 1968, and H1N1 in 2009 – and before COVID-19 many scientists were predicting that the next pandemic would be caused by a flu virus.

One case of avian influenza A(H5) was reported in the United States in April 2022, and Ecuador reported its first case on January 9, 2023.

H5N1 is considered a special pathogen, as there are no effective medical countermeasures to prevent or treat infection.

Prompt identification of a suspected case of H5N1, isolation, and supportive care measures are essential.

Additionally, there may be evidence for the use of the antiviral treatment oseltamivir, which is used for other influenza A viruses.

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