Vaccine efficacy and duration of protection

Why do immunocompromised people need an additional dose of COVID-19 vaccines?

An additional dose of a vaccine is recommended for immunocompromised people for all COVID-19 vaccines with WHO Emergency Use Listing.

Individuals with immunocompromising conditions and those receiving immunosuppressive therapy often do not develop an adequate immune response to a standard primary series of COVID-19 vaccination. Therefore in these cases an additional dose in the primary series is needed to optimize or enhance the immune response and thereby increase effectiveness against disease.