Salk, who died in 1995, is remembered Tuesday around the medical world; there's even a Google doodle perched atop its search page. But the more telling illustration is the accompanying graph, which shows the sharp and virtually permanent drop in polio incidence in the U.S. after mass vaccination began. The Salk vaccine was declared safe and effective in 1955. An oral vaccine developed by Albert Sabin was first tested in 1957 and went into widespread use in 1963