Although the number of cases of H1N1 influenza have declined since a peak in the week ending October 24, 2009, it is not over until it is over.

An excerpt of this CDC report notes that “all three 20th century influenza pandemics (in 1918, 1957 and 1968) multiple waves of intensity were observed.”

January and February are the months when influenza activity increases. H1N1 remains dominant. Vaccination still is encouraged.

CDC  MMWR

“Editorial Note

“As of January 9, 2010, the vast majority of influenza activity this season had been from 2009 H1N1. Activity was highest during the week ending October 24, 2009, and has since declined. The number of influenza-associated pediatric deaths reported to date for the 2009–10 season (236) is more than three times the average number (74) reported for the 2005–06, 2006–07, and 2007–08 influenza seasons. Resistance to antiviral neuraminidase inhibitors has been low among the 2009 H1N1 viruses, and the vast majority of 2009 H1N1 viruses tested remain related to the A/California/7/2009 (H1N1) reference virus selected by WHO as the 2009 H1N1 vaccine virus.

“January and February are months during which seasonal influenza activity usually increases; thus, increased influenza activity from 2009 H1N1 viruses, seasonal influenza viruses, or both might occur in the remainder of the influenza season. In all three 20th century influenza pandemics (in 1918, 1957, and 1968), multiple waves of influenza activity were observed (3). The 2009 H1N1 virus is likely to continue to circulate through the winter months, resulting in more cases, hospitalizations, and deaths. ..”

Source: CDC Morbidity and Mortality Weekly Report, January 22, 2010, analysis of influenza activity through January 9, 2010