WHO Announces 2 Strain Changes For 2020 Southern Hemisphere Flu Vaccine

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Last February - when the WHO normally decides on which strains to put in this  fall's Northern Hemisphere vaccine - they opted to delay their decision on the H3N2 component for 30 days (see WHO: (Partial) Recommended Composition Of 2019-2020 Northern Hemisphere Flu Vaccine).

At issue was the sudden rise of H3N2 clade 3C.3a reported in North America (and other places), which had started last fall's season as a minor component of what appeared on track to being a relatively mild H1N1 season.

By early 2019 we'd switched into a moderately severe H3N2 season with clade 3C.3a leading the pack (see CDC HAN #0418: Influenza Season Continues with an Increase in Influenza A(H3N2) Activity).

In late March the WHO decided to switch to the surging Clade 3C.3a H3N2  virus, betting that it would become the dominant H3 strain worldwide by this fall. 

Only, that doesn't appear to have happened.  At least, not yet.

Three weeks ago in the latest ECDC Influenza surveillance report (see Influenza Virus Characterisation, July 2019), I noted that H3N2 clade 3C.3a  - while rising slightly compared to the June report - had yet to take off in Europe as it did last winter in North America.  Nor did it dominate Australia's now receding 2019 flu season.

While it is still possible H3N2 clade 3C.3a could break bad again this winter - right now clade 3C.2a1b viruses continue to dominate globally - and that poses a couple of immediate concerns.

• First, this fall's Northern Hemisphere's flu vaccine may not provide as good of a match to the circulating H3N2 viruses as originally hoped. 

• Second, given the six month lead time needed for vaccine production, decisions must be made now about what H3 clade to include in next year's Southern Hemisphere vaccine.

Welcome to the maddening, high stakes game of trying to figure out what a growing array of global influenza viruses will do 6 to 12 months in the future.  And be very glad it isn't your job to make these decisions.
 
This week the World Health Organization brought together representatives from GISRS (Global Influenza Surveillance and Response System), along with members of OFFLU (the OIE/FAO Network on Animal Influenza), and other experts to recommend what flu strains to include in next year's Southern Hemisphere flu vaccine.

I've reprinted their summary (changed strains I've highlighted in red). I'll have a bit more after the break:

Recommended composition of influenza virus vaccines for use in the 2020 southern hemisphere influenza season

27 September 2019

It is recommended that quadrivalent vaccines for use in the 2020 southern hemisphere influenza season contain the following:

• an A/Brisbane/02/2018 (H1N1)pdm09-like virus;
• an A/South Australia/34/2019 (H3N2)-like virus;
• a B/Washington/02/2019-like (B/Victoria lineage) virus; and
• a B/Phuket/3073/2013-like (B/Yamagata lineage) virus.
  

It is recommended that trivalent influenza vaccines for use in the 2020 southern hemisphere influenza season contain the following:

• an A/Brisbane/02/2018 (H1N1)pdm09-like virus;
• an A/South Australia/34/2019 (H3N2)-like virus; and
• a B/Washington/02/2019-like (B/Victoria lineage) virus.
  

For more information

27 September 2019: Recommended composition of influenza virus vaccines for use in the 2020 southern hemisphere influenza season - full report pdf, 496kb

The failure of clade 3C.3a to dominate as expected raises the possibility that - once again - we'll have a less-than-stellar vaccine against H3N2 flu this winter.  But this is but one of four strains included in the vaccine, and H3N2 may not dominate this year's flu season. 

Good H3N2 match or not, I'm glad I've got my shot already, as even a poorly matched vaccine can provide some protection.

H3N2 - which arrived as a pandemic strain in 1968 - has been in circulation now for more than 50 years. Over that time it has had to reinvent itself innumerable times (via antigenic drift) to evade acquired immunity, resulting in an increasing number of subclades of the virus co-circulating around the globe.

As our global society becomes increasingly mobile in this 21st century, so too do the viruses we carry. While this has obvious pandemic implications, it also makes seasonal flu more volatile, complex, and unpredictable. 

As influenza viruses become more antigenically diverse, the job of picking viruses to include in next season's flu vaccine will only become more difficult.

Credit NIAID

All of which makes the development of a`universal' flu vaccine (see J.I.D.: NIAID's Strategic Plan To Develop A Universal Flu Vaccine) of greater importance than ever.

We should see the WHO's twice-annual zoonotic flu vaccine recommendations released shortly.