Newborn babies are very sensitive and particularly vulnerable face up to infections. The absence of immunization at birth makes the newborn very vulnerable. Certainly, the processus of immunization starts very quickly (less than 48 hours after birth), but the progress is very long. So, the newborn is exposed to a risk if the hygiene surrounding is not good.
Elderly or disabled people
The immunization phenomenon and immunosuppression phenomenon make elderly and sick people more sensitive to some germs. We have to be vigilant to not contaminate them and to help them, if needed, to keep a good hygiene.
Pregnant women, even healthy ones, must be vigilant to avoid contracting diseases which can have bad consequences on the development of their children. Elementary precautions consist of having a good hygiene but also a good diet.