Nearly $6 billion has been allocated. Clinical trials are entering a crucial third phase, and Operation Warp Speed is getting closer to the goal of delivering 300 million doses of a COVID-19 vaccine by January. But when Americans line up for their immunizations, the vaccine they receive might not be what they expect. The popular notion of a vaccine — a shot in the arm that prevents diseases such as measles, polio or shingles for years or a lifetime — may not apply. Under recently released federal guidelines, a COVID-19 vaccine can be authorized for use if it is safe and proves effective in as few as 50% of those who receive it. And "effective" doesn't necessarily mean stopping people from getting sick from COVID-19. It means minimizing its most serious symptoms, experts say. “We should anticipate the SARS-CoV-2 vaccine to be similar to the influenza vaccine,” said Dr. Kathleen Neuzil, director of the Center for Vaccine Development at the University of Maryland. “That vaccine may or may not keep people from being infected with the virus, but it does keep people out of the hospital and the ICU.”