Having Employees Return to Duty Act of 2021 or the HERD Act of 2021 This bill addresses federal employees who comply with Executive Order 14043 (requiring COVID-19 vaccination for federal employees). Specifically, the bill requires each federal agency, with respect to each agency employee who has complied with such order, to require the employee to work from that employee's duty station and to work the hours required as of February 15, 2020. If such an employee was not employed by the applicable agency as of that date, that requirement shall apply to the employee with respect to duty station and hours of the individual who occupied that position as of that date. An agency may implement different policies than, or supplemental policies to, those requirements, including by requiring social distancing at a particular work site, if the agency finds that (1) there is substantial transmission of COVID-19 within a community in which such requirements would otherwise be carried out, as determined by the Centers for Disease Control and Prevention; and (2) implementing those different or supplemental policies will not degrade the level of service that the agency provides to the public.