经我查证，疫苗加强针，在英文中比较常见的表述为：COVID-19 booster vaccine，新闻报道中也常简写为：booster shot， booster dose 或者直接用 boosters。

所谓疫苗加强针（booster shot/booster dose），是指在常规使用疫苗剂型、剂量注射后，额外增加的疫苗接种。这里的核心词booster，来源于动词boost，主要表示“加强、促进、推动”等意思，比如boost production（促生产），boost morale（提振士气）等，在这里表示“increase or renew the effect of the vaccine”，即“增强疫苗产生的效果”。

以下是我摘录了英语新闻中出现“加强针”的表述原句供参考：

1. Boosters are recommended to maintain immunity against COVID-19.

2.Booster doses for 16 and 17 year olds

If you are 16 or 17 (or have turned 16 since you had your primary dose of COVID-19 vaccine) you can have the Pfizer vaccine as a booster dose.

Booster doses for people aged 18 years and older

If you are aged 18 years or older, you can have the Pfizer or Moderna vaccine as a booster dose regardless of which vaccine you had for your first 2 doses.

3.Benefits of a booster dose

Two doses of COVID-19 vaccine provide very good protection, especially against severe disease. People who are severely immunocompromised need 3 doses.

A booster dose will make sure the protection from your first doses is even stronger and longer lasting, and should help prevent spread of the virus.

A booster dose increases your protection against:

infection with the virus that causes COVID-19

severe disease

dying from COVID-19.

A booster dose will continue to protect you, your loved ones and your community against COVID-19.

Booster doses are free for everyone.

【双语例句】

If immunity against the virus wanes in the long run, these memory cells can be "reawakened effectively" by delivering a booster shot and this will "produce very good protective effects", Shao said.

如果在比较长的时间后，身体对病毒的免疫能力逐渐下降，可以通过注射加强针重新唤起体内的这些记忆细胞，并产生非常好的保护效果。