FLU UPDATE – Southern Hemisphere Flu Coming Soon

A sadistic annual ritual that Fitzpatrick Translational Science engages in is predicting the efficacy of the seasonal influenza virus vaccine. How do we predict this? Here’s the short answer: what happens in the southern hemisphere does not stay there; it travels north to us here in the United States.

The WHO (World Health Organization) publishes extensive international influenza data via www.who.int/flunet. They publish the recommended composition of an influenza virus vaccine in March for the northern hemisphere for the upcoming flu season (which we are now in), and vaccines are distributed in August. Here is a list of vaccine efficacy for the past 17 years:

While we do not yet know how many unvaccinated people will be affected in the US, the big question begins with the particularly evil A strain that first appeared in 2009. The A (H1N1) pdm09 virus brought on the first pandemic the US has had since 1968. This virus is the predominant flu virus circulating in the southern Asia. As you can see by this graph from the WHO, nearly all flu specimens are H1N1 pdm09.


Data source: FluNet (www.who.int/flunet). Global Influenza Surveillance and Response System (GISRS). Data generated on 09/18/17.

Fortunately, the H1N1 strain is NOT the dominant Type A strain in tropical South America (the not-so-bad H3 subtype is). So, which Type A flu strains are going to cause havoc in the U.S.? Will it come from southern Asia or South America?

In a 2015 publication by Baumgartner (Emerg Infect Dis), the authors compared flu virus strains from North and South America from 2001-2014. They found that in 92% of the seasons, the predominant A (H1N1) strain in South America was also guilty of being the predominant A (H1N1) strain in North America. While it is likely that the South American H1N1 strain will head towards the U.S., it is a small fraction of the overall flu specimens (at least in the current flu season).

Data source: FluNet (www.who.int/flunet). Global Influenza Surveillance and Response System (GISRS). Data generated on 09/14/17.

The 2017-18 North American vaccine composition DOES include an A (H1N1) strain in both the trivalent and quadrivalent vaccines. As the WHO and CDC found out following the 2009-10 Pandemic*, this strain is “remarkably different from the classic seasonal influenza H1N1 viruses and the viruses used to prepare vaccines.” (Baldo V. 2016 J Prev Med Hyg). The question remains, how much mutation will occur in the prevalent United States A (H1N1) strain, although we know it has been the predominant circulating strain in southern and southeast Asia?

There is no certainty that this past Spring’s dominant flu strain in South America will invade us here in the United States, but it’s worth betting on. Our Evidence-based flu season prediction is that the H1N1 pdm09 strain will indeed make its presence in the US, but will be in the minority of flu specimens (much like what recently happened in South America). Overall, we predict a likely mild season.

As for influenza vaccine matching (for efficacy this flu season):
  • A/Michigan/45/2015 (H1N1)pdm09-like virus: It is included in the vaccine, but this virus is known for rapidly mutating and circulating viruses were poorly inhibited by people who have had the vaccine, so efficacy is probably not so good. 

  • A/Hong Kong/4801/2014 (H3N2)-like virus: The lineage is not determined by the WHO, but it’s antigenically similar to prevailing A 3C.2a strains that have been seen in many countries – so efficacy is probably good.

  • B/Brisbane/60/2008-like virus: The lineage is similar to B/Victoria/2/87 - so probably good efficacy.

  • B/Phuket/3073/2013-like virus (in quadrivalent vaccines): The lineage is similar to B/Yamagata/16/88 – so probably good efficacy.

Kevin Fitzpatrick, Fitzpatrick Translational Science

* The CDC has identified the following flu seasons as “Pandemic” (a global outbreak of a new influenza A virus that is very different from current and recently circulating human seasonal influenza A viruses):
  • 1918 H1N1 that 1/3 of the world’s population became infected with and killed 500 million people world-wide

  • 1957 H2N2, also called “the Asian Flu”, that killed 1.1 million people worldwide

  • 1968 H3N2 that killed 1 million people worldwide

  • 2009 H1N1 (pdm09) that killed up to 575,000 people worldwide

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