The U.S. Department of Health and Human Services' Office of Inspector General in 2020 concluded that the proposal could violate the kickback law by inducing patients to buy Pfizer's drug while leaving taxpayers to bear the costs.
Pfizer sued the department to challenge its determination. The Manhattan-based 2nd U.S. Court of Appeals last July ruled in favor of the government, rejecting Pfizer's argument that a subsidy program would violate the anti-kickback law only if it were administered with corrupt intent.

An interesting case for sure. Basically Pfizer offering to pay for the copay component of the treatment will saddle Medicare with the rest of the costs. Since more patients will presumably be then induced to take the drug, Pfizer is effectively increasing its addressable market into low income families but shifting the cost of the drug into the government.