Group B streptococci (GBS) are known to cause life-threatening disease in some newborns, but are commensals in the adult female vagina. Which of the following helps to explain why GBS acts as a pathogen in newborns and as a commensal in healthy adults? To be marked correct, you'll need to select all applicable statements, as there may be more than one correct answer.

a. Adults are regularly vaccinated against GBS, whereas newborns have not yet received this vaccination.

b. Newborns have reduced immunity compared to healthy adults.

c. Newborns lack firmly established normal flora that compete with the opportunistic pathogen

d. The only known portal of entry for GBS is urogenital.