In a single (unvaccinated) family one winter, the 12-year-old
and 4-year-old came down with chickenpox. The mother and father had
experienced the disease as children and were unaffected this
time. The 3-month-old baby did not become ill, either.
However, 4 months later the baby exhibited a shingles
outbreak. Using immunological phenomena, explain what was
likely going on with the baby.