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From Wild Influenza Virus Sample to Seasonal Vaccine

We provide insights from the strain recommendation and share how we develop our seasonal vaccines.

Strain Selection Insights - three vials

Every year, twice a year the World Health Organization (WHO) recommends the influenza virus strains to be included in the upcoming seasonal influenza vaccines that are produced and supplied to the global markets.

The recommendation is based on influenza surveillance data from the WHO Global Influenza Surveillance and Response System (GISRS), a network of institutions, collaborating centres and virus reference laboratories in 124 WHO member states.

In late February, based on its surveillance data, the WHO announced the four seasonal influenza virus strains for both egg-based and cell-based vaccines deemed to be best matched to protect against influenza circulating in the community for the 2022/23 Northern Hemisphere winter. Quadrivalent seasonal vaccines produced by Seqirus contain two influenza A strains and two B strains. The WHO recommended strains for the Northern Hemisphere 2022/23 seasonal influenza vaccine are:

Egg-based vaccines

  • an A/Victoria/2570/2019 (H1N1)pdm09-like virus;
  • an A/Darwin/9/2021 (H3N2)-like virus;
  • a B/Austria/1359417/2021 (B/Victoria lineage)-like virus; and
  • a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus.

Cell culture- or recombinant-based vaccines

  • an A/Wisconsin/588/2019 (H1N1)pdm09-like virus;
  • an A/Darwin/6/2021 (H3N2)-like virus;
  • a B/Austria/1359417/2021 (B/Victoria lineage)-like virus; and
  • a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus.

Why do the vaccines change season to season?

Beverly Taylor, Head of Influenza Scientific Affairs at Seqirus, explained that influenza viruses are constantly mutating which is why the seasonal influenza vaccine is reformulated each season to target the most prevalent strains of influenza circulating in the community.

According to a report by the WHO, recommended strains for inclusion in the Northern Hemisphere 2022/23 vaccine are the same as those included in the Southern Hemisphere 2022 seasonal influenza vaccine, except there are two different strains from the last Northern Hemisphere 2021/22 season vaccine recommendation.

What’s in a name?

With a global network of over 150 National Influenza Centres (NICs), seven WHO Collaborating Centres (CCs), four Essential Regulatory Laboratories, and 13 H5 Reference Laboratories, the Centres for Disease Control and Prevention (CDC) evidences why it is important to have a consistent catalogue in place for the wild virus samples collected.

Let’s take a look at an example to understand the global naming convention for the seasonal vaccine strains:

  1. The first term indicates the type of influenza virus, A or B
  2. The next term is the geographical origin of the wild virus sample and may correspond to a country, city, region e.g. Darwin, Austria, Phuket, Wisconsin, Victoria, etc.
  3. The third item corresponds to the reference number of the strain
  4. Followed by the year the virus was isolated
  5. Last, and in brackets, are the numbers of the hemagglutinin (H) and the neuraminidase (N) formula

From wild virus to vaccine

Not all vaccine virus candidates are equal when it comes to manufacturing which is why the WHO recommend virus strains for both egg-based and cell culture- or recombinant-based vaccines.

The CDC explains that even before confirming the formulation of the seasonal vaccine, the WHO collaborating centres supply the candidate vaccine virus (CCV) seeds to manufacturers so they can be evaluated, developed, screened and optimised. At Seqirus, our Technical Development and Manufacturing Sciences and Technology teams take these steps in an effort to get the virus seeds ready to be used in manufacturing as well as to generate the materials to be used in testing the vaccine.

With the seasonal clock ticking, we need to plan ahead

Knowing the limited window of time each season available to produce and supply a seasonal vaccine, our planning at Seqirus for the season starts well before the WHO confirms the vaccine composition.

Under the guidance of Beverly Taylor, we track the virus surveillance across three manufacturing sites throughout the year, gathering information and intelligence from the WHO, collaboration centres and the WHO released bi-weekly reports. Based on the intelligence gathered, the Global Operations team conducts an at-risk manufacturing assessment with the goal to be able to ‘bank’ batches of bulk virus production in advance of the announcement for the strains less likely to change.

Strain selection is one part of the unique and complex process of bringing a flu vaccine to market each season. Across three continents, a global network of over 1700 Operations and Quality employees, supported by a full range of business partners, work together to safely deliver the differentiated Seqirus portfolio of cell, egg-based and adjuvanted seasonal influenza vaccines to customers around the world. To learn more about the Seqirus manufacturing network, click here.