Although it is often claimed that China is preoccupied with economic growth to the exclusion of all else, the fact that it has sought to minimize the flow of production factors without hesitation to contain the epidemic—with the government still maintaining a tight rein even though the epidemic situation in the country has been displaying a positive trend—should drive home the message that such measures are crucial, and how imperative it is that the decision is made to adopt them at the earliest date.

红体部分为主干，为了简洁，how从句没有全部标红。

即The fact should drive home A and B. [drive home意思请查字典]

A与B为“名词结构“，A=the message that such measures are crucial, B=how imperative it is that the decision is made to adopt them at the earliest date.

B句为how+adj引导的感叹性名词从句，it是形式主句，指代后面的that从句

 我的理解是：the message that such measures are crucial, and  (that) how imperative it is that the decision is made to adopt them at the earliest date.  such measures... and how imperative....两个部分都是message的同位语，也就是说message 引导了两个并列的同位语从句，how 前面省略了that. 

how imperative 为感叹句，对此其它老师已有解答，这里不再重复。

Although...，the fact (...) should drive home the message ( that...)，and (how...).

and后面的句子和前面的that such measures are crucial是并列的,都是对message的解释说明，属于同位语从句。

how imperative it is不做什么成分吧，它是个完整的句子，类似感叹句的句型，加强语气。后面的that有的人认为是同位语从句，是对前面的it的解释说明（有人说这样说是不对的因为同位语从句是对名词的解释说明不能解释代词），有人说它就是对前面的代词it的补充说明，也有的人说it是形式主语，后面的that...是真正的主语，也就是It is imperative that the decision is made to adopt them at the earliest date. 然后把that前面的部分变成了感叹句的句型。