1918 and 2009 H1N1 Similarities Confirm Recombination

The new Nature report also assessed the immune response of different groups to the new virus. The most intriguing finding, according to Kawaoka, is that those people exposed to the 1918 virus, all of whom are now in advanced old age, have antibodies that neutralize the H1N1 virus. "The people who have high antibody titers are the people born before 1918," he notes.

The above comments are in association with an upcoming publication in Nature demonstrating that patients born prior to 1918 still have antibodies that not only neutralize the 1918 pandemic virus, but also cross react with the 2009 pandemic swine H1N1. Similarly, the 2009 pandemic strain replicates more efficiently in the lungs of experiment mice and ferrets, which may explain the frequent deaths of previously healthy young adults. The targeting of this age group also parallels data from 1918.

These data further support the observation that the 90% of the polymorphisms in sequences of all 8 gene segments from the 1918 pandemic strain can be found in a human H1N1 isolate, WSN/33 or a swine H1N1 isolate, A/swine/Iowa/15/1930. These data support a scenario that mimics the data for 2009, which involves a swine H1N1 moving into a human population and spreading efficiently.

Data worldwide identify previously healthy young adults dying from the pandemic H1N1 infection. However, as the swine H1N1 spreads throughout the human population, opportunities for adaption to human host arise via acquisition of human polymorphisms. Interestingly, many of the new acquisitions of can be found in early H1H1 isolates, raising additional concerns that the 2009 pandemic H1N1 is following a path similar to the evolutionary path of 1918.

A recent isolate from Japan, A/Sapporo/1/2009 has a genetic HA backbone matching the recent oseltamilvir resistant isolate A/Hong Kong/1269/2009, but has acquired a new polymorphism found in WSN/33 as well as an additional polymorphism found in swine/Iowa/15/1930, further supporting evolution along the 1918 pathway.

Thus, the growing list of similarities between 2009 pandemic H1N1 and 1918 pandemic H1N1 continues to cause concern.