D.C. Mun. Regs. tit. 22, r. 22-B132
Each student under seven (7) years of age who receives his or her primary immunization shall have either oral poliovirus vaccine (OPV) or inactivated polio vaccine (IPV) administered according to §§ 132.2 to 132.6.
The first dose shall be administered no earlier than six (6) weeks of age and not later than two (2) months of age.
The second dose shall be administered no earlier than four (4) weeks after the first dose and not later than two (2) months after the first dose.
The third dose shall be administered two (2) months after the second dose and by nineteen (19) months of age, but no earlier than four (4) weeks after the second dose.
A supplementary fourth dose shall be administered at four (4) years of age and by the fifth birthday, but no earlier than four (4) weeks after the third dose. If the third dose of a primary series of all OPV or all IPV was given on or after four (4) years of age, a fourth dose shall not be required. If the fourth dose was given before four (4) years of age and not earlier than four (4) weeks after the third dose, no additional dose shall be required.
If a combination of OPV and IPV doses are administered as part of a series, a total of four (4) doses shall be administered, regardless of the student's present age or the student's age at administration of the primary series. The fourth dose shall be administered no earlier than four (4) weeks after the third dose.
D.C. Mun. Regs. tit. 22, r. 22-B132