What Problems Could Be Encountered When Practicing Variolation to Protect

What problems could be encountered when practicing variolation to protect against smallpox? (Select all that apply)

A) approximately 1% of patients developed active smallpox disease and died
B) some patients suffered an allergic reaction to the variolation process
C) variolation is only effective in younger people
D) while variolated patients were developing their immunity, they were highly contagious and represented an epidemic threat