All the children in a given school year are vaccinated as a cohort.
For example, children may receive the oral polio vaccine in Year One of primary school (about six or seven years of age), the BCG in Year Six, and the MMR in Form Three of secondary school.
"Vaccination is unique among de facto mandatory requirements in the modern era, requiring individuals to accept the injection of a medicine or medicinal agent into their bodies, and it has provoked a spirited opposition.
This opposition began with the first vaccinations, has not ceased, and probably never will.
To eliminate the risk of disease outbreaks, at various times governments and other institutions established policies requiring vaccination.