evidence: Children who have never received a COVID-19 vaccine should follow this schedule: [...] People who have a weakened immune system and received previous COVID-19 vaccines should get at least one updated vaccine dose. They can get additional updated doses at least two months after the last updated vaccine dose if recommended by their provider. People who have a weakened immune system and have never received a COVID-19 vaccine should get three vaccine doses as part of their initial vaccine series. They can then get additional doses, as noted above.