Credit ACIP/CDC
#18,377
Although there are no guarantees that avian H5N1 will spark the next pandemic, its recent global surge, its new found affinity for infecting dairy cattle, and its recent spillover into at least 3 dozen farm workers in the United States has it very high on our watch list.
H5N1 has loomed large before - only to recede - and that could happen again, but over the past 20 years we've seen many nations (including the United States) stockpile relatively small quantities of H5N1 pre-pandemic vaccines.
Since these vaccines have a limited shelf life, and these avian viruses continue to evolve, it is impractical to stockpile large quantities. As new clades and variants appear the WHO & CDC Work to Develop Candidate H5N1 Vaccines, and to date more than three dozen H5 CVVs have been selected by WHO for development.
Most of those candidate vaccine viruses are now extinct, making this an expensive proposition, but having an already approved CVV can save weeks or even months of valuable time if mass production and distribution of a vaccine are ever required.
We've already seen signs that changes to the HA surface protein - particularly with the case in Missouri - may render existing vaccines less effective. Six weeks ago the CDC wrote:
The HA gene sequence confirms that the virus is clade 2.3.4.4b, and the NA sequence was confirmed as N1. There are two amino acid differences in the HA that have not been seen in sequences from previous human cases. These amino acid differences are not known to be associated with changes to the virus's ability to infect and spread among people. However, both differences are in locations that may impact the cross-reactivity of clade 2.3.4.4b candidate vaccine viruses (CVVs).A
Admittedly, even a `good match' with a pandemic strain might not be all that protective against infection, although it would hopefully reduce the severity of a breakthrough infection. H5 vaccines have a reputation for being relatively poorly immunogenic, often requiring an adjuvant or very high amounts of antigen to elicit a good immune response.
Complicating matters, we've also seen difficulties in producing bulk H5N1 vaccines in the past, particularly in egg-based production facilities (see Manufacturing Pandemic Flu Vaccines: Easier Said Than Done).
Having a pandemic vaccine will be critically important, but it is highly unlikely to be a panacea for a pandemic. Particularly since a novel influenza virus might undergo rapid changes over the course of a pandemic, requiring frequent updates to any vaccine.
Today one of the best science writers in the business - Maggie Fox - has an opinion piece in Scientific American on why an H5N1 vaccine may be slow in coming. It deserves reading in its entirety, so I've simply provided the link.
Highly recommended.
OCTOBER 30, 2024
6 MIN READ
A Bird Flu Vaccine Might Come Too Late to Save Us from H5N1
If the influenza virus infecting cattle workers starts a pandemic, help in the form of a vaccine is months away
BY MAGGIE FOX