When to leave out の?


> マスク大手 24時間態勢で増産 新型ウイルス肺炎感染拡大で  
>

_from[here](https://www3.nhk.or.jp/news/html/20200121/k10012253491000.html)_

In this sentence the words 新型 and ウイルス form the meaning "a new type of virus".
But shouldn't 新型 be connected using の? I have seen this pattern a lot of
times, but when are you allowed to leave out the particle?

