#17,924
In addition to deciding which influenza virus components to include in the seasonal flu vaccine, twice each year flu researchers meet with the WHO to discuss the development of new CVVs (Candidate Vaccine Viruses) for zoonotic influenza.
Just as there are a growing number subclades of seasonal H3N2 and H1N1 jockeying for dominance in the flu world (see the ECDC's Influenza virus characterization - Summary report, Europe, January 2024), there are dozens of continually evolving subclades and genotypes of avian and swine flu viruses competing in the wild.
When we speak about an avian H5 virus, or a swine H1 virus - we are actually talking about an array of genetically distinct variants - each on their own evolutionary path. And a vaccine developed against one strain of the same subtype may not prove protective against another.
Although it can be expensive, having a proven CVV already tested and approved can save months of valuable time if mass production and distribution of a pandemic vaccine is ever required.
Today's WHO report describes recent detections of a variety of novel H5, H9, H10, and H1 flu viruses with zoonotic potential around the world, and recommendations for new CVVs.
While no new H5, H9, or H10 CVVs were recommended, over the past six months seen a number of novel swine-origin H1 viruses emerge around the world, including Eurosurveillance: A Case of Swine Influenza A(H1N2)v in England, November 2023.
Three A(H1N1)v virus infections were identified; one each in Brazil (clade 1A.3.3.2 5 ), Spain (clade 1A.3.3.2) and Switzerland (clade 1C.2.2). The cases from Spain and Switzerland reported exposure to swine; no swine exposure was reported for the case from Brazil. The case from Brazil was severe, those from Spain and Switzerland were mild and all individuals recovered. An A(H1N2)v (clade 1B.1.1.1) virus infection was detected in the United Kingdom of Great Britain and Northern Ireland. The individual had mild disease and did not report exposure to swine.
A summary of recent A(H1) activity in swine and humans is shown in Table 4.
Genetic and antigenic characteristics of influenza A(H1)v viruses
Although virus isolation is pending or was unsuccessful from the four A(H1)v virus infections, sequence analysis showed varying levels of HA similarity to existing zoonotic CVVs or seasonal vaccine reference viruses. The A(H1)v viruses were most similar to swine viruses detected in the relevant countries or regions.
Recent clade 1A.3.3.2 viruses from swine that are genetically similar to the virus causing the human infection n Spain (A/Catalonia/NSAV198289092/2023) (Fig. 1), reacted poorly to post-infection ferret antisera raised against existing A(H1N1)pdm09 vaccine reference viruses (Table 5) and adult human sera. No CVVs for clade 1A.3.3.2 swine viruses are available.
(SNIP)
Influenza A(H1)v candidate vaccine viruses
Based on the current genetic, antigenic, and epidemiologic data, new CVVs that are antigenically like A/Catalonia/NSAV198289092/2023 and A/England/234600203/2023 are proposed. The available and pending A(H1)v CVVs are listed in Table 7.
