It is not clear why there is so little flu, particularly swine flu, going around, experts say. “Surely there’s a sufficient number of people who haven’t been infected or vaccinated,” said Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota.
Many scientists say the answer probably has to do with how the flu virus progresses. Influenza comes and goes in waves, normally running from October through May. But pandemic viruses—new viruses that emerge and spread quickly around the globe—often move to a different rhythm, and can reach their busiest stage at unusual times like summer and early fall, although the reason for this isn't understood.
More via H5N1: US: A very odd flu season.