This does not imply that the vaccine did produce such side effects. It refers to placebo recipients only, and does not address the discrepancy, which involves only vaccine recipients.

This is irrelevant information. There is no indication that participants self-reported their symptoms, so this difference in attribution between the groups would not have affected the study.

This does not explain why people who received the vaccine developed hepatitis A symptoms. The discrepancy is not between the two groups, but between the vaccine's complete effectiveness and the hepatitis A symptoms among the people who received it.

This resolves the apparent paradox by explaining that vaccine recipients were infected prior to inoculation. It is consistent because the author gives no information about the vaccine's effect on patients already infected with hepatitis A.

This does not explain how vaccine recipients developed symptoms in the first place. If the vaccine is completely effective, patients who received it should not have contracted hepatitis A.