Friday, September 25, 2020

WHO Recommended 2021 Southern Hemisphere Flu Vaccine Composition & Impact Of COVID-19 On Selection

Flu Reports Flat-lined Since Late March - Credit WHO 

#15,473

Over the past several months (see here, here, and here) we've looked at the dearth of influenza reported globally since the emergence of COVID-19 last spring, and speculated on how that might adversely affect the selection of virus components for next year's Southern Hemisphere flu vaccine. 

This week the World Health Organization has convened an expert committee to select vaccine strains, and this afternoon they have released their recommendations (see below).

First the announcement, then a look at their statement on how the COVID-19 pandemic has complicated decisions for next year's (and possibly beyond) flu vaccine.

Recommended composition of influenza virus vaccines for use in the 2021 southern hemisphere influenza season
25 September 2020
It is recommended that quadrivalent vaccines for use in the 2021 southern hemisphere influenza season contain the following:
Egg-based Vaccines
an A/Victoria/2570/2019 (H1N1)pdm09-like virus;
an A/Hong Kong/2671/2019 (H3N2)-like virus;
a B/Washington/02/2019 (B/Victoria lineage)-like virus; and
a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus.

Cell- or recombinant-based Vaccines
an A/Wisconsin/588/2019 (H1N1)pdm09-like virus;
an A/Hong Kong/45/2019 (H3N2)-like virus;
a B/Washington/02/2019 (B/Victoria lineage)-like virus; and
a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus.
It is recommended that trivalent influenza vaccines for use in the 2021 southern hemisphere influenza season contain the following:
Egg-based Vaccines

an A/Victoria/2570/2019 (H1N1)pdm09-like virus;
an A/Hong Kong/2671/2019 (H3N2)-like virus; and
a B/Washington/02/2019 (B/Victoria lineage)-like virus.

Cell- or recombinant-based Vaccines

an A/Wisconsin/588/2019 (H1N1)pdm09-like virus;
an A/Hong Kong/45/2019 (H3N2)-like virus; and
a B/Washington/02/2019 (B/Victoria lineage)-like virus.
 
For more information

25 September 2020: Recommended composition of influenza virus vaccines for use in the 2021 southern hemisphere influenza season - full report pdf, 478kb
 
25 September 2020: Frequently Asked Questions pdf, 216kb

From the accompanying Q&A, the following changes have been made to the Southern Hemisphere 2021 flu vaccine recommendations since the last vaccine:

  • For the A(H1N1)pdm09 vaccine virus component, replacement of the A/Brisbane/02/2018-like virus with an A/Victoria/2570/2019-like virus for egg-based production and an A/Wisconsin/588/2019-like virus for cell-based production, is recommended.
  • For the A(H3N2) vaccine virus component, replacement of the A/South Australia/34/2019-like virus with an A/Hong Kong/2671/2019-like virus for egg-based production and an A/Hong Kong/45/2019-like virus for cell-based production, is recommended.
The new recommendations also differ slightly from the current Northern Hemisphere Flu Vaccine:
  • For the A(H1N1)pdm09 vaccine virus component, replacement of the A/Guangdong-Maonan/SWL1536/2019-like virus with an A/Victoria/2570/2019-like virus for egg-based production and replacement of the A/Hawaii/70/2019-like virus with an A/Wisconsin/588/2019-like virus for cell-based production, is recommended.
  • The other viruses recommended for production of trivalent and quadrivalent 2021 southern hemisphere vaccines are the same as recommended for the 2020-2021 northern hemisphere vaccine.
Normally flu experts would have thousands of antigenically characterized flu samples taken over the past 6 months from around the world to base their decisions on, but as we've seen (see WHO Influenza Update #376), virus submissions have been running about 1/100th of normal.

This paucity of flu surveillance data, and its impact on vaccine component selection, is addressed in 3 sections of today's Q&A document. 

15. What impact has the COVID-19 pandemic had on the GISRS influenza
surveillance?

Influenza surveillance was disrupted during the early stages of the COVID-19 pandemic resulting in substantial decreases in the numbers of specimens tested for influenza and subsequent shipments of viruses to WHO CCs of GISRS compared with the corresponding period in previous years. Reporting directly or indirectly to FluNet by some countries was also delayed or stopped. Some countries were less affected and maintained strong influenza
surveillance as demonstrated by the detection of human cases of zoonotic influenza.
In order to address the persistent public health threat from influenza and maintain global influenza surveillance and response capabilities while responding to the COVID-19 pandemic, an interim WHO guidance document was published to prepare GISRS for the upcoming influenza seasons
From June 1 to August 30 of this year, 107 countries, areas, or territories reported data to the global influenza surveillance platform FluNet – 132 countries, areas, or territories reported data over the same period in 2019. In addition, countries are exploring the use of influenza surveillance systems for COVID-19 sentinel surveillance.
16. What impact has the COVID-19 pandemic had on influenza activity?
The COVID-19 pandemic has had a major impact on influenza activity. Between February and March 2020, influenza activity was elevated in most countries in the northern hemisphere consistent with a typical influenza season. Starting in mid-March, influenza activity decreased sharply, concomitant with the spread of SARS-CoV-2. Implementation of travel restrictions, mitigation strategies and social-distancing measures is likely the reason for decreased influenza activity. Correspondingly, very low levels of influenza detection have been reported globally, including from countries in the temperate zone of the southern hemisphere.

17. How has the COVID-19 pandemic impacted the 2021 southern hemisphere influenza vaccine recommendation?

The amount of genetic and antigenic data available from recently circulating viruses has been significantly lower for this southern hemisphere vaccine recommendation meeting than is typical due to the COVID-19 pandemic. Influenza activity had started in several northern hemisphere countries prior to the emergence of the COVID-19 pandemic, providing a source of viruses collected in 2020, mainly from February and March. While the overall numbers were lower, recent viruses from every WHO region were characterized and the recommendations are based on viruses that are likely to be a fair representation of those that may continue to circulate.

Nevertheless, due to the reduced number of recent viruses circulating and available for characterization, there are uncertainties regarding the full extent of genetic and antigenic diversity. It is unknown what impact the low level of influenza activity will have on forthcoming influenza seasons and which influenza virus types and subtypes will begin to circulate widely when social interactions resume. 

Between `viral interference' from SARS-CoV-2, and pandemic inspired social distancing and NPIs (hand hygiene, face covers, etc.), the global `fluscape' has been radically altered since early spring.  Exactly what this might mean for the emergence of novel flu viruses is unknown. 

But the natural evolution of seasonal flu viruses has also been impacted in ways that we can only begin to envision (see COVID-19, The Next Flu Season, And The Temporary Immunity Hypothesis), and for the most part, this is all happening out of our sight. 

Whether seasonal flu returns this winter, next summer - or stays suppressed for a year or longer - we should be prepared for some surprises when it finally does return.  If nothing else, community immunity to influenza will likely diminish the longer this lull continues. 

While COVID-19 is our number one priority today, history suggests that influenza is unlikely to take a back seat for very long. 


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