Answer :
According to the American Psychological Association [APA] code of ethics, the researcher is violating the principle of: informed consent.
What is informed consent?
Informed consent states that a client or patient should have enough information about the medical care they are going to receive from a health practitioner before allowing the practitioner to care for them.
Based on the given scenario the researcher violated the principle of informed consent because he did not disclose that the vaccine may have side effect.
Therefore the researcher is violating the principle of: informed consent.
Learn more about informed consent here:https://brainly.com/question/26830148
#SPJ1