World Health Organization (WHO) officials have sounded alarm bells following the death of an 11-year-old girl in Cambodia from the deadly H5N1 strain of avian influenza, the first such death in the country in nearly 10 years. 

At least 12 people in Cambodia have now been tested for infection with H5N1 following the girl’s death, WHO officials said at a press briefing on Friday. 

WHO officials said the organization was in direct contact with Cambodian public health authorities at the time of the briefing. Cambodia is closely watching the girl’s father, who was also infected, as well as her other contacts, in an effort to determine if person-to person transmission of the deadly virus may have occurred.

The H5N1 strain of Avian influenza has only occasionally infected humans, and mostly as a result of animal-to-human contact. 

But public health officials have long been concerned that a new strain of the virus, harbored by poultry and other birds around the world, could eventualy emerge that is more easily transmissible between people.   

‘Worrying’ says WHO official

“The situation is worrying,” said Dr Sylvie Briand, WHO’s director of epidemic and pandemic preparedness and prevention. The press conference was supposed to provide an update on the composition of seasonal flu vaccines, but was largely taken over by concerns about the more deadly and unpredictable H5N1 pathogen.

The virus has had a fatality rate of over 53% among the 868 cases recorded worldwide between 2003 and November 2022. 

But so far documented cases of human-to-human transmission have been exceedingly rare, and there is no evidence of sustained human transmission of the virus, according to WHO officials.   

“So far, it is too early to know if it’s human-to-human transmission or exposure to the same environmental conditions,” Briand said.

Case in Cambodia follows one in China last year  

The case in Cambodia follows a similar case of H5N1 in China in September 2022, also in an infected girl who ultimately succumbed to the virus.  It was the first case of avian influenza to be recorded in China since 2015.  

The disease is spreading rapidly among bird populations. Since the start of last year, over 200 million birds worldwide were culled or died as a result of the disease, according to the World Organisation for Animal Health.

Genomic sequence not yet known, but vaccines are on hand

The genomic sequence of the exact strain that infected the girl is still unknown. But it is most likely one of two clades, said Dr Richard Webby, Director of WHO’s Collaborating Centre for Studies on the Ecology of Influenza in Animals. 

The two dominant clades of the virus reported by Cambodian authorities in recent years include Clade 2344B, which has ravaged bird flocks across Europe, Africa and the Americas, and Clade 2321C, circulating in Cambodia and the surrounding South Asia region.  

Many of the tools needed to respond to the H5N1 threat already exist, including multiple vaccines and antivirals, said Dr Wenqing Zhang, Head of WHO’s Global Influenza Programme at the briefing. He said that in addition to five vaccines, nearly 20 products are licensed for pandemic use.

WHO has recommended an update the existing reference vaccine, which will begin production in the coming weeks. While it will take some time before the newest vaccine is deployed, Zhang said the vaccines contained in pre-existing international stockpiles built up after an H5N1 outbreak in 2003 stoked fears of a pandemic, have also produced promising clinical trial results against circulating strains. 

If an outbreak occurs, “there is going to be a period of time when the perfectly matching vaccine won’t be available,” Webby said. “That’s when the stockpiled vaccines could perhaps come into play and probably offer offer protection from more severe disease.”

But Webby noted that the trials were not definitive proof of real world efficacy.

“We need to separate in vitro reactivity of people’s antibodies from vaccine effectiveness,” he said.

Image Credits: Roee Shpernik.