Medical Supplies for Pandemics Act of 2021 This bill requires the Department of Health and Human Services (HHS) to take specified actions, as part of its management of the Strategic National Stockpile, to establish and maintain domestic reserves of critical medical supplies. Specifically, HHS must (1) create incentives for domestic manufacturers of medical supplies to increase emergency stocks and diversify geographic production; (2) purchase, lease, or enter into joint ventures with respect to facilities and equipment to produce medical supplies; and (3) work with distributors to refresh and replenish medical supplies. HHS must also submit a report to Congress concerning the details of any purchase, lease, or joint venture. The department's authority under the bill to make purchases, leases, or joint ventures for medical supplies terminates on September 30, 2024.