(a) classes of aliens ineligible for visas or admission
Except as otherwise provided in this chapter, aliens who are inadmissible under the following paragraphs are ineligible to receive visas and ineligible to be admitted to the United States:
- In general Any alien —
- who is determined (in accordance with regulations prescribed by the Secretary of Health and Human Services) to have a communicable disease of public health significance; 
- except as provided in subparagraph (C), who seeks admission as an immigrant, or who seeks adjustment of status to the status of an alien lawfully admitted for permanent residence, and who has failed to present documentation of having received vaccination against vaccine-preventable diseases, which shall include at least the following diseases: mumps, measles, rubella, polio, tetanus and diphtheria toxoids, pertussis, influenza type B and hepatitis B, and any other vaccinations against vaccine-preventable diseases recommended by the Advisory Committee for Immunization Practices,
- who is determined (in accordance with regulations prescribed by the Secretary of Health and Human Services in consultation with the Attorney General) —
- to have a physical or mental disorder and behavior associated with the disorder that may pose, or has posed, a threat to the property, safety, or welfare of the alien or others, or
- to have had a physical or mental disorder and a history of behavior associated with the disorder, which behavior has posed a threat to the property, safety, or welfare of the alien or others and which behavior is likely to recur or to lead to other harmful behavior, or
- who is determined (in accordance with regulations prescribed by the Secretary of Health and Human Services) to be a drug abuser or addict,
- is inadmissible.
- Waiver authorized — For provision authorizing waiver of certain clauses of subparagraph (A), see subsection (g) of this section.
- Exception from immunization requirement for adopted children 10 years of age or younger Clause (ii) of subparagraph (A) shall not apply to a child who
- is 10 years of age or younger;
- is described in subparagraph (F) or (G) of section 1101 (b)(1) of this title;  and
- is seeking an immigrant visa as an immediate relative under section 1151 (b) of this title,
if, 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 provisions of subparagraph (A)(ii) 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 identified in such subparagraph.