December 2-5 is National Influenza Vaccination Week in the US. This year the push to immunize against flu comes as the disease has begun to increase substantially throughout the United States. A substantial rise in the number of influenza cases typically does not occur until the end of December in the US. The last time that the disease incidence rose so early was in 2003-04. That was one of the most lethal seasons in 35 years, with 48,000 deaths.