Influenza vaccines are the best weapons we’ve got against a disease that each year kills as many as a half-million people, including 3,000 to 49,000 Americans. Yet this season’s worse-than-usual flu in the U.S. underscores the limitations of the existing vaccines.
Shortcomings include the inability to rapidly expand vaccine supply in the event of an especially bad flu and the need to vaccinate people with a new formulation almost every year as the virus mutates. These are problems enough when it comes to coping with the regular seasonal flu. They spell potential disaster in the case of pandemic flu, which occurs sporadically (most recently in 2009) when an animal strain of the virus jumps to humans.