Vaccines are highly, but not perfectly, effective. The definition is the same, it's the adjective that's changing. For true immunity without anyone else needin

Vaccines are highly, but not perfectly, effective. The definition is the same, it's the adjective that's changing. For true immunity without anyone else needing to be vaccinated they'd need to be perfectly effective. Since they're not, more of the community needs to be vaccinated. The less effective they are (or the more widespread or infectious the virus is) the larger the proportion of the population that needs to be vaccinated becomes.