Chapter 2 - Medical Examination and Vaccination Record
The results of the medical examination and vaccination record determine whether an applicant is inadmissible on health-related grounds. The medical examination documentation indicates whether the applicant has either a Class A or Class B medical condition and the vaccination record shows whether the applicant has complied with all vaccination requirements.
Class A and B conditions are defined in Department of Health and Human Services (HHS)regulations. 
Class A conditions are medical conditions that render a person inadmissible and ineligible for a visa or adjustment of status.  A Class A medical condition is a:
Communicable disease of public health significance per HHS regulation;
A failure to present documentation of having received vaccinations against vaccine-preventable diseases; 
Present or past physical or mental disorder with associated harmful behavior or harmful behavior that is likely to recur; and
Drug abuse or addiction.
Class B conditions are defined as physical or mental health conditions, diseases, or disability serious in degree or permanent in nature.  This may be a medical condition that, although not rendering an applicant inadmissible, represents a departure from normal health or well-being that may be significant enough to:
Interfere with the applicant’s ability to care for himself or herself, to attend school, or to work; or
Require extensive medical treatment or institutionalization in the future.
When a medical examination is required to determine the applicant’s admissibility, the person must be examined by a physician who is designated to perform this examination.
By statute, any medical officer in the U.S. Public Health Service may conduct the examination. However, this rarely occurs. Most medical examinations are conducted by a physician designated as a civil surgeon by USCIS  or designated as a panel physician abroad by the U.S. Department of State (DOS). Civil surgeons complete medical examinations for applicants in the United States, while panel physicians complete medical examinations for immigrant visa and refugee applicants seeking immigration benefits from outside the United States.
[^ 3] This Class A medical condition only applies to noncitizens who seek admission as immigrants, or who seek adjustment of status to one lawfully admitted for permanent residence. Additionally, a child who is adopted and under the age of 10 years or younger is not deemed to have a Class A condition if the following conditions apply: Prior to the admission of the child, an adoptive parent or prospective adoptive parent of the child, who has sponsored the child for admission as an immediate relative, has executed an affidavit stating that the parent is aware of the vaccination requirement , and will ensure that, within 30 days of the child’s admission, or at the earliest time that is medically appropriate, the child will receive the vaccinations required for immigration purposes. See 42 CFR 34.2(d)(2).