Then both groups were vaccinated with a chickenpox vaccine.是什么意思？

Then both groups were vaccinated with a chickenpox vaccine.

然后两组都接种水痘疫苗.

then

adv. 那时，然后，那么，话说回来；adj. 当时的，那时的；

例句
Liz adjusted her mirror and then edged the car out of its parking bay.
莉兹调了调后视镜，将车子挪出了停车位。

both

adj. 二者，两者都；pron. 二者；adv. 二者，二者都；conj. 不仅…而且…，…和…都；

例句
The gym can be used by both able-bodied and disabled people.
这家健身房健全和残障人士都可使用。

groups

n. 组( group的名词复数 )，群，小型流行音乐演奏组，集团；v. 使成群，集合( group的第三人称单数 )，分类，归类；

例句
All-male groups will not be accepted.
清一色的男性团体将不被接纳。

were

be的过去时复数和第二人称单数形式，有时代替 was,用于条件从句、动词 wish 之后等；

例句
Shops, houses, and vehicles were set ablaze.
店铺、房子和车辆全都陷于火海。

vaccinated

adj. [医]已接种的，种痘的，接种过疫菌的；v. 给…接种疫苗( vaccinate的过去式和过去分词 )，注射疫苗，接种疫苗；

例句
Dogs must be vaccinated against distemper...
狗必须接种犬瘟热疫苗。

with

prep. 和，跟，随着，关于，和…一致；

例句
A waiter entered with a tray...
侍者端着托盘进来了。

chickenpox

n. 水痘；

例句
Thomas came down with chickenpox at the weekend.
托马斯周末染上了水痘。

vaccine

n. 疫苗，痘苗；adj. 痘苗的，疫苗的；

例句
When he tested an early vaccine on himself, some described the act as foolhardy...
当他在自己身上试验还处在初级阶段的疫苗时，有些人说他的行为是蛮干。