Vaccine boosters are not unusual. CNN's medical analyst explains why

With the Biden administration expected to announce that booster doses will be needed for most people who received the Covid-19 vaccine, many people have questions: Are boosters safe? Does the fact that we may need boosters mean that the vaccine isn't working? And who should get them?

source https://www.cnn.com/2021/08/17/health/why-boosters-covid-wen-wellness/index.html