No. An additional dose is different from a booster dose.
Some people, those who are immunocompromised, may not develop the same immune response level after vaccination as others. An additional dose of the same type is recommended for those individual to help them build the same level of immunity as people who are not immunocompromised. This is part of the primary schedule for immunocompromised individuals.
In contrast, a booster dose is given when a person has completed their vaccine schedule and protection against the virus has decreased over time.