A new strain of H5N1 avian flu could emerge that would result in human-to-human transmission.

a. Why is vaccine development not the highest priority right now?

b. Once an epidemic has started, vaccine development will be a high priority. Epidemics often occur in “waves” of illness, with different segments of the population becoming ill each time. Three waves of disease, each lasting weeks, are not rare in a flu epidemic. Why does creating a vaccine in preparation for a second wave of an epidemic make the most sense?