Extant blood samples to deduce the strains of the 1890 and possibly earlier pandemic influenzas.

Influenza outbreaks in 1918, 1957 and 1968 caused some of the highest infectious disease mortality in the 20th century. In particular the 1918 pandemic caused more than 50 million deaths worldwide-the most deaths caused by any infectious disease ever in human history. Influenza pandemics in 1890 and earlier in the 19th century and back until at least the 16th century also caused non-trivial mortality. The excessively high mortality from flu in these years is thought to be due to major antigenic shifts in influenza strains, as opposed to smaller drifts in flu strains in years between pandemics. It is also thought that flu strains cycle naturally; however, as the 1918 pandemic was caused by an H1N1 strain, the 1957 pandemic by an H2N2 strain and the 1968 pandemic by an H3N2 flu, there have not been sufficient strains in an era when they could be evaluated molecularly to prove natural flu cycling in the human population. We have searched databases and institutions and here report finding extant preserved samples of sera of sufficient age and drawn at appropriate times to elucidate the strain of the 1890 pandemic and possibly shed light on influenza strains prior to that.