Laboratory-confirmed influenza, Australia, 01 January 2016 to 12 September 2021
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As depicted by the red flat-line across the bottom of the above graph, influenza rates fell off a cliff after COVID-19 emerged in the early spring of 2020, resulting in the genetic sequencing of vastly fewer seasonal flu viruses (see ECDC: Influenza Virus Characterisation - July 2021) over the past 18 months.
While having fewer influenza viruses in circulation should lead to fewer mutations - and therefore less antigenic drift - it isn't out of the question that a `drifted' flu virus could lead the charge when seasonal flu finally does return.
Regardless of the limited data available, every 6 months global flu experts must meet to determine the composition of the next flu vaccine; each winter for the next Northern Hemisphere fall vaccine, and each autumn for the following year's Southern Hemisphere's vaccine.
This week long consultation - sponsored by the WHO - also produces a semi-annual roster of Candidate Vaccines For Pandemic Preparedness, the most recent of which will be released later this week.
Today we have the announced composition of the 2022 Southern Hemisphere Flu vaccine, which contains two changes from the Northern Hemisphere Flu vaccine, which is currently being distributed north of the equator. From the WHO FAQ:
The following updates to the vaccine have been recommended:
- For the A(H3N2) vaccine virus component, replacement of the A/Cambodia/e0826360/2020-like virus with A/Darwin/9/2021-like and A/Darwin/6/2021-like viruses for egg- and cell culture-based production, respectively, is recommended.
- For the B/Victoria vaccine virus component, replacement of the B/Washington/02/2019-like virus with a B/Austria/1359417/2021-like virus is recommended for both production systems.
The other viruses recommended for production of trivalent and quadrivalent 2022 southern hemisphere vaccines are the same as recommended for the 2021/2022 northern hemisphere vaccine.
Recommended composition of influenza virus vaccines for use in the 2022 southern hemisphere influenza season
24 September 2021
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Overview
It is recommended that quadrivalent vaccines for use in the 2022 southern hemisphere influenza season contain the following:
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- 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.
It is recommended that trivalent influenza vaccines for use in the 2022 southern hemisphere influenza season contain the following:
Egg-based vaccines
- an A/Victoria/2570/2019 (H1N1)pdm09-like virus;
- an A/Darwin/9/2021 (H3N2)-like virus; and
- a B/Austria/1359417/2021 (B/Victoria lineage)-like virus.
Cell- or Recombinant-based vaccines
- an A/Wisconsin/588/2019 (H1N1)pdm09-like virus;
- an A/Darwin/6/2021 (H3N2)-like virus; and
- a B/Austria/1359417/2021 (B/Victoria lineage)-like virus
The WHO describes the impact that the COVID pandemic has had on influenza activity, and data collection, which they say brings additional `uncertainties' to the flu seasons ahead.
How has the COVID-19 pandemic impacted the 2022 southern hemisphereinfluenza vaccine recommendation?The volume of data available from recently circulating influenza viruses and the geographic representation have been significantly lower for this southern hemisphere vaccine recommendation meeting than was typical prior to the COVID-19 pandemic. The reduced number of characterised viruses raises uncertainties regarding the full extent of the genetic and antigenic diversity of currently circulating influenza viruses and those likely to pose a threat in forthcoming seasons. Nevertheless, new groups of A(H3N2) and B/Victoria-lineage viruses were identified that had spread internationally and showed antigenic changes compared to recently recommended vaccine viruses. Consequently, the A(H3N2) and B/Victoria-lineage component recommendations have been updated.
Of course, even in years where surveillance isn't compromised by a global health crisis, it is possible for an antigenically `drifted' flu virus to rise to dominance between the time the vaccine is created, and the arrival of the next flu season (see 2014's CDC HAN Advisory On `Drifted’ H3N2 Seasonal Flu Virus).
Despite the uncertainties about whether influenza will return this fall, and whether the dominant strains will match the components in the current vaccine, it still makes sense to get the flu vaccine.
Our lack of daily exposure to seasonal respiratory viruses - either due to our wearing face masks and social distancing, or to `viral interference' by the COVID virus - have left our immune systems less able to fend off colds and flus.
Hence the reports we are seeing this summer of a steep rise in RSV globally, and from the UK of the `Worst Cold Ever', even though we've seen no evidence that the respiratory viruses there have changed.
Getting the flu shot should - at least temporarily - ramp up your immune system, and that could reduce your risks of infection, or severe illness, regardless of the respiratory viruses circulating (see COVID-19, The Next Flu Season, And The Temporary Immunity Hypothesis).
While flu vaccines are far from perfect, and can’t promise 100% protection, it – along with practicing good flu hygiene (washing hands, covering coughs, & staying home if sick) – remain your best strategy for avoiding the flu and staying healthy.While limited, there is also growing evidence suggesting Flu Vaccination May Offer Some Protection Against COVID Infection.
