For individuals with moderate to severe immunocompromise, CDC states that, beyond the primary series, additional doses of 2023–2024 COVID-19 vaccine may be administered (with a minimum two-month interval) based on the clinical judgment of the individual’s healthcare provider and personal preference and circumstances.
The option to receive these additional doses is offered because vaccine effectiveness declines most rapidly in people with moderate to severe immunocompromise. Such people also have the highest risk of hospitalization with COVID-19 if infected. Although protection against severe disease is more durable than protection against milder illness, individuals in these groups may benefit from shorter intervals between doses.
See CDC’s interim immunization schedule for details: www.cdc.gov/vaccines/covid-19/downloads/COVID-19-immunization-schedule-ages-6months-older.pdf.