Wednesday, March 10, 2021

WHO: Candidate Vaccine Viruses for Pandemic Preparedness - March 2021


Credit NIAID


Twice each year influenza experts gather to discuss recent developments in human and animal influenza viruses around the world, and two weeks ago the WHO announced their Recommended composition of influenza virus vaccines for use in the 2021 - 2022 northern hemisphere influenza season.

This week they have published their recommendations for new candidate vaccine viruses for pandemic preparedness. 

Although surveillance and reporting of seasonal flu and novel flu viruses with zoonotic potential - which is required by the WHO IHR 2005 - is patchy even during the best of times, since the start of the COVID-19 pandemic we've seen even less data than usual (see Flying Blind In the Age Of Pandemics & Emerging Infectious Diseases).

This scarcity of data was addressed in the WHO's Q&A document provided with this year's Northern Hemisphere vaccine recommendations.
18. How has the COVID-19 pandemic impacted the 2021-2022 northern hemisphere influenza vaccine recommendation? 

The volume of data available from recently circulating influenza viruses and the geographic representation have been significantly lower for this northern hemisphere vaccine recommendation meeting than is typical.
The reduced number of viruses available for characterization raises uncertainties regarding the full extent of the genetic and antigenic diversity of circulating influenza viruses and those likely to pose a threat in forthcoming 9 seasons. Nevertheless, new groups of A(H3N2) viruses were identified, some of which had spread internationally. Consequently, the A(H3N2) component recommendation has been updated.
Just as there are a growing number subclades of seasonal H3N2 and H1N1 jockeying for dominance in the flu world (see ECDC: Influenza Virus Characterisation, November 2020), there are dozens of 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 really 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.

Over the past 2 decades more than 5 dozen H5, H9, H1, H3, and H7 candidate vaccine viruses (CVVs) have been selected by WHO for development. Many of these older CVVs are for viruses that no longer circulate in the wild, having been supplanted by newer versions.

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.

In their last report - released in October of 2020 - the WHO called for two new CVVs be developed; one for Avian A(H5N6) clade isolated in Vietnam, and the other for a Eurasian avian-like A/H1N1 clade 1C.2.2 swine virus detected in Germany.

EA H1N1 swine-origin viruses have been on our radar for the past 6 years but gained further prominence last summer after as study published in PNAS (see Eurasian Avian-like H1N1 Swine Influenza Virus With Pandemic Potential In China) reported a greater than 10% seroprevalence for the EAH1N1 virus among swine workers tested, suggesting that EAH1N1 is gaining human infectivity.

Some recent blogs on this development include:

While EA H1N1 remains very high on our watch list, since then we've received news of a new H5 avian virus (H5N8) jumping species (see WHO Statement & Risk Assessment On Human Infection with Avian H5N8 – the Russian Federation), mildly infecting 7 poultry workers in Russia.  

We've also seen a spike in H5N6 infections in China (see China's Recent Resurgence Of Human HPAI H5N6 Infections), and the largest HPAI H5 Epizootic in 4 years (see ECDC Update: Avian Influenza Epizootic In Europe - December 2020 - February 2021).

Making it of little surprise that in their latest update, the WHO proposes a CVV for the (now zoonotic) H5N8 virus, along with another EA H1N1 virus (A/Netherlands/10370-1b/2020). 

The 15-page WHO report contains detailed information on these, and other, influenza A viruses with zoonotic potential, and the candidate vaccine viruses under development around the globe.  I've only included some brief excerpts, so follow the link to read it in its entirety.

Antigenic and genetic characteristics of zoonotic influenza A viruses and development of candidate vaccine viruses for pandemic preparedness March 2021

 The development of influenza candidate vaccine viruses (CVVs), coordinated by WHO, remains an essential component of the overall global strategy for influenza pandemic preparedness. 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. Zoonotic influenza viruses continue to be identified and evolve both genetically and antigenically, leading to the need for additional CVVs for pandemic preparedness purposes. Changes in the genetic and antigenic characteristics of these viruses relative to existing CVVs and their potential risks to public health justify the need to select and develop new CVVs. 

This document summarises the genetic and antigenic characteristics of recent zoonotic influenza viruses and related viruses circulating in animals1 that are relevant to CVV updates. Institutions interested in receiving these CVVs should contact WHO at or the institutions listed in announcements published on the WHO website2

(Continue . . . )

While we are making progress against the COVID pandemic, the fact remains that novel and seasonal flu evolution continues unabated, meaning the seeds of the next pandemic or public health crisis could already be sown somewhere in the world.