La Nina and Influenza Pandemics

A new study published in PNAS by Jeffrey Shaman and Marc Lipsitch finds that the four recent influenza pandemics (1918, 1957, 1968, and 2009) were all preceded by La Niña (colder sea surface) conditions in the Pacific Ocean. The authors suggest that the climate changes can alter migratory bird activity and thus possibly impact their mixing with domestic animals. They therefore hypothesize that La Niña results in a higher likelihood of divergent influenza subtypes coming together with a subsequent higher probability of emergence of novel "pandemic" influenza strains.

In an accompanying BBC story by Richard Black, professor Shaman explains the findings and also cautions that the link should not yet be used to predict pandemics. However, he is hopeful that increased influenza strain surveillance subsequent to recent novel H1N1 and avian H5N1 activity will soon be able to confirm whether their proposed hypothesis is correct.

Reference
Shaman and Lipsitch PNAS 1/17/2012

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