1. You should get a booster shot to stay protected.
你应该接种加强针以保持免疫力。

2. The clinic is offering a booster shot to all eligible adults.
诊所向所有符合条件的成年人提供加强针接种。

A: Do I need a booster shot now?
A：我现在需要接种加强针吗？

B: Yes, it has been six months since your last dose.
B：是的，距离你上次接种已经六个月了。

1) 加强针

2) 追加剂量

1. 加强针

e.g.
A booster shot helps maintain your immunity.
加强针有助于维持你的免疫力。

noun phrase

1. An extra dose of a vaccine to increase immunity.