Thursday, March 02, 2023

CDC Update On Cambodian H5N1 Cluster


It's another day and there are unconfirmed media reports of another H5N1 case in China (see FluTracker's thread), but so far I've not been able to find anything to corroborate these reports. I know Sharon Sanders has an email in to the WHO, and hopefully we'll get clarification sooner rather than later. 

Regardless of the details of this latest report, additional cases will likely turn up in the weeks ahead.

For those who have been along for much of this ride over the past 20 years, you know we've been here before, and that today's handful of H5N1 cases pale in comparison to the thousands of human H5 & H7 infections we've seen in the past (see graphic below).

Officially, there have been 870 human H5N1 infections, 84 H5N6 infections, and nearly 1,600 H7N9 infections.  All of these are likely under counts, and these numbers don't include the scores of H9N2 and sporadic human infections with H7N4, H10N3, H3N8, H7N2, etc. that have been reported. 

The period between 2013 and mid-2017 saw the highest number of human infections with (H7 & H5) avian flu, averaging several hundred each year.  In a few cases, H-2-H transmission appears to have occurred. 

Luckily, these viruses were far better at jumping from poultry to people, than from human-to-human. The concern is that these viruses - as they occasionally spillover into humans and other mammals - could pick up host adaptations that will allow the virus to spread more efficiently among humans. 

Despite the hyperbolic tabloid headlines screaming about mutations, and `possible human-to-human spread', genetic analysis has not found evidence for either of these concerns.   

This update, published yesterday, from the CDC. 

Update on H5N1 Bird Flu in Cambodia
EspaƱol | Other Languages | Print

March 1, 2023— This update provides results of a preliminary assessment of the H5N1 virus identified in the first of two human infections detected in Cambodia in 2023 based on its genetic sequence and gives an update on the epidemiological investigation.

On February 26, 2023, the Cambodian Ministry of Health shared the full genetic sequence of the H5N1 virus recovered from the patient who died in that country on February 22, 2023. CDC has conducted a preliminary analysis of the genetic sequence of that H5N1 bird flu virus. This is an H5N1 virus from clade, which is different from the H5N1 viruses now spreading in U.S. wild birds and poultry, which are from clade 
This virus is similar to past viruses detected in that geographic area over recent years. The genetic sequence suggests that an existing clade candidate vaccine virus (CVV), called NIBRG-301 (A/duck/Vietnam/NCVD-1584/2012-like) would offer protection against the virus identified in Cambodia. 

Additionally, there were no genetic changes identified that are known to be associated with increased ability to spread to people or reduced susceptibility to influenza antiviral drugs. CDC has requested virus samples from both cases in Cambodia in order to conduct additional laboratory testing/analysis to confirm these and other characteristics of the viruses and to provide a more detailed risk assessment.

CDC continues to support the Ministry of Health, Ministry of Agriculture, Animal, Forestry and Fisheries, and Ministry of Environment, in its ongoing One Health investigation. Evidence to date continues to support the conclusion that these two human infections are the result of two instances of bird-to-human spread

There is still no indication of person-to-person spread associated with these two cases. The investigation has revealed that both patients became sick at about the same time and were likely exposed to sick or dead poultry prior to becoming ill, including being near sick/dead poultry kept in a coop under the house or through butchering, cleaning, and cooking chicken that died. Investigation and containment efforts continue, including monitoring and/or testing of contacts of the two cases for 10 days after their last exposure, along with active surveillance for influenza-like-illness in the village. CDC will provide additional updates as needed.

This is an update to a spotlight originally posted on February 25, 2023.

H5N1 is a genuine pandemic threat, but it is far from the only one we are watching. H5N6 continues to evolve,  MERS-CoV still emerges from time to time in the Middle East, and there are literally dozens of other potential contenders (see CDC IRAT list).  

Regardless of the source, we need to be ready for the next pandemic.  Because ready or not, it will come. It is only a matter of time.