H5 Clade Diversity Around the Globe – Credit WHO
From time to time, the World Health Organization makes recommendations on new candidate influenza vaccine viruses (CVVs) for investigation and consideration, in case one of these emerging viruses begins to show pandemic potential. The last time we looked at this was early in the Winter of 2014 (see Moving Viral Targets), where the WHO proposed that 2 new (H5N1 & H9N2) candidate vaccine viruses be developed.
Influenza A viruses are categorized by two proteins they carry on their surface; their HA (hemagglutinin) and NA (neuraminidase), resulting in subtypes like H5N1, H7N9, or H3N2.
While the list continues to expand, currently we know of 18 different HA proteins and 11 different NA proteins, making many different subtype combinations possible, although many of these combinations have yet to be observed in nature.
Within each strain, there are often genetic groupings called clades, and within each clade- subclades – and within each of these, many variants may exist. And over time these clades, subclades, and variants may evolve antigenically enough away from its predecessors to require a reformulated vaccine.
Over the past decade more than two dozen H5N1 candidate influenza vaccine viruses have either been developed or proposed, and with the recent emergence of H5N8, H5N2, H5N3 and H5N6 and the continued evolution of H5N1, that roster continues to grow.
This week, the WHO’s Weekly Epidemiological Record (WER) published a new review of currently circulating zoonotic influenza viruses, and their recommendations for two new vaccine virus candidates (both H5’s), one based on the recent changes observed in Egypt’s H5N1 virus, and the other based on the recent introduction of H5N8 into North America.
The development of representative candidate influenza vaccine viruses CVVs, coordinated by WHO, remains an essential component of the overall global strategy for pandemic preparedness.
Zoonotic influenza viruses continue to be identified and often evolve both genetically and antigenically, leading to the need to update CVVs for pandemic preparedness purposes. Changes in the genetic and antigenic characteristics of these viruses, their relationship to existing CVVs, and the associated potential risks for public health, justify the need to select and develop new CVVs.
Selection and development of CVVs are the first steps towards timely vaccine production and do not imply a recommendation for initiating manufacture. National authorities may consider the use of one or more of these CVVs for pilot lot vaccine production, clinical trials and other pandemic preparedness purposes based on their assessment of public health risk and need.
This document summarizes the genetic and antigenic characteristics of recent zoonotic influenza viruses and related viruses circulating in animals, and updates information on the availability of CVVs. Institutions that wish to receive these CVVs should contact WHO at email@example.com or the institutions listed in announcements published on the WHO website
Influenza A(H5) candidate vaccine viruses
Based on the available antigenic, genetic and epidemiologic data, A/Egypt/N04915/2014-like (clade 2.2.1) and A/gyrfalcon/Washington/41088-6/2014-like (clade 18.104.22.168) CVVs are proposed. The available and pending A(H5) CVVs are listed in Table 5. National authorities may consider the use of one or more of these A(H5) CVVs for pilot lot vaccine production, clinical trials and other pandemic preparedness purposes based on their assessment of public health risk and need. As the viruses continue to evolve, new A(H5) CVVs may be developed.
This document also reviews H7N9, H9N2, H5N6, and various swine variant (H1N1v, H3N2v) activity around the globe, and determines that no additional CVVs are required for these viruses at this time.