If this is true best stack up on your supply of antiviral drugs, because there would be an above-average chance of experiencing another influenza pandemic during the approaching northern hemisphere spring or summer of 2012 (as indeed La Niña is back).

But considering the question mark behind the title of their publication in PNAS today the two researchers from Columbia University and Harvard would agree the connection between La Niña episodes and influenza pandemics does at least appear a bit farfetched.

Besides, last year was about the strongest La Niña in decades and nothing special happened that boreal summer either, did it?

The authors do however seem to have a strong empirical case to suggest La Niñas and flu pandemics may be linked – and they have a theory.

The four big influenza pandemics

There have been four big influenza pandemics in recent history. The first was the ‘Spanish’ flu pandemic, which started with the 1918 outbreak of a H1N1 virus. This pandemic may have killed as many as 50 million people – for a large part because public health had greatly deteriorated after the four exhausting years of the First World War.

The fourth pandemic is the greatly hyped ‘Mexican’ flu, or [but this risks to insult our pink friends] the swine flu pandemic of 2009 – also of the H1N1 strain.

In between there were large outbreaks in 1957, the Asian Flu (H2N2 virus – 1.5-2 million deaths), and in 1968, the Hong Kong Flu, from the H3N1 virus strain, which killed approximately one million people.

The swine flu probably got us all, killed some 20,000 people – and left the rest of us not only largely unharmed, but also improved our collective immune system to resist new attacks by resembling H1N1 viral mutations.

[As novel H1N1 flu outbreaks can indeed be very deadly – deadly enough to also categorise this story under Demography – it means for the world population as a whole the swine flu pandemic of 2009 can actually be considered a gift from above, as it has harnessed us.]

The link to La Niña episodes

Now the researchers noticed that all of these flu pandemics started in the boreal spring or summer and were preceded by La Niñas – the phases in the El Niño Southern Oscillation (ENSO) that see large upwelling of cold deep ocean water in the East Pacific, which is then spread out across much of the ocean.

Now here’s their theory:

“Changes in the phase of the El Niño–Southern Oscillation have been shown to alter the migration, stopover time, fitness, and interspecies mixing of migratory birds, and consequently, likely affect their mixing with domestic animals. We hypothesize that La Niña conditions bring divergent influenza subtypes together in some parts of the world and favor the reassortment of influenza through simultaneous multiple infection of individual hosts and the generation of novel pandemic strains.”

They also note that bird migration routes determine the chances of these birds making contact with human livestock and that “gene-swapping between avian and pig influenza viruses was a factor in the 2009 swine flu pandemic.”

The researchers state further testing of the hypothesis* is required.

[*) Other La Niña theories have been researched more. One noteworthy after effect of the 2010-2011 La Niña could be the drought in the Horn of Africa – which occurs in an ENSO-related cycle as well.]

[By the way – ‘He who controls ENSO’ in the title of this story is the person who progresses furthest in research into geoengineering La Niña.]

© Rolf Schuttenhelm | www.bitsofscience.org