Preparing for the next influenza pandemic: lessons from multinational data.

Background: In the past decade, avian influenza has made several incursions of increasing scope and virulence into humans. The likelihood of another pandemic is increasing with time. In work recently published, influenza was found to be the principal cause of the increase in mortality in the United States during the winter months. In a companion report, the U.S. national vaccination program was shown to have increased coverage of high risk groups 5-fold from 1980 to 1999, but excess mortality did not decline in any elderly age group. The Multinational Influenza Seasonal Mortality Study has assembled and has begun to mine mortality data from many countries. Early results indicate that the U.S. results extend to other economically developed countries and probably worldwide.

Results: The Multinational Influenza Seasonal Mortality Study data extend the observations of others that there were heralding events that provided advance warning for all of the pandemics of the 20th century. Moreover, in the first year of emergence of A(H3N2) viruses, the 1968-1969 pandemic produced little excess mortality outside of North America. It appears that there were at least 2 variants of the pandemic virus, differing at 1 or more internal gene loci, and that the more virulent form emerged as dominant in the second pandemic season.

Conclusions: Integrating these findings, it seems clear that the influenza control strategy now used in about 50 countries is less than optimal. While it is likely that there will be more time to react in the pandemic season than previously imagined, an enhancement of the historical strategy is clearly indicated. Furthermore, the vaccine shortage that is presently inevitable suggests that a departure from the historical strategy if calamitous ineffectiveness is to be avoided.