Which of the following best defines variolation as it was historically practiced for smallpox?

Why did exposure to cowpox protect people from smallpox and how is that reflected in the origin of the word "vaccine"?

A clinical vaccine candidate is able to replicate in host cells at low levels without causing disease symptoms. According to vaccine classification principles, which category does this candidate belong to and what is a likely clinical implication?

A virus has a basic reproduction number (R0) estimated at 5.0. Using the herd immunity threshold formula, what minimum fraction of the population must be immune to interrupt sustained transmission, and what implication does that have for an eradication campaign?

Infants receive maternal antibodies that can blunt responses to some vaccines. Which synthesized strategy best mitigates maternal antibody interference while still protecting neonates from severe disease?