D.C. Mun. Regs. tit. 22, r. 22-B142
A student who has not received a primary immunization with an all IPV or all OPV series shall receive a total of three (3) vaccine doses. Each dose shall be administered not less than four (4) weeks apart.
OPV or IPV doses administered before the age of seven (7) may satisfy § 142.1, unless given before the appropriate age or at less than the required minimum interval between doses.
If a combination of OPV and IPV doses are administered as part of a series, a total of four (4) doses are required, regardless of current age or age at administration of primary series. The fourth dose shall be administered no earlier than four (4) weeks and not later than eight (8) weeks after the third dose.
For each student eighteen (18) years of age or older, the polio immunization vaccine is recommended but not required.
D.C. Mun. Regs. tit. 22, r. 22-B142