If a provider already received payment from an underinsured individual, are they required to reimburse that individual after receiving payment from the program?

Yes. The program reimburses providers for COVID-19 vaccine administration fees for underinsured individuals; therefore, any money collected from the individual must be returned to the individual if the provider received funding for that patient through this program.
This requirement is included in the Terms and Conditions that the provider signs in order to enroll in the program.