No vaccines are 100% effective. Take the flu vaccine for example. Does it prevent you 100% from getting the flu? No, never has. It's generally 30-40% effective and it will help reduce the severity if you do get it. Some vaccines are more effective than others. The idea is to get enough of the population vaccinated to reduce the spread and severity of the disease.
https://www.immune.org.nz/vaccines/e...-effectiveness