Unlikely that Covid came from Wuhan lab, WHO says

[GoodTaste]

I don't understand why "that" should be used here. "Unlikely - Covid came from Wuhan lab, WHO says" Or "Covid unlikely came from Wuhan lab, WHO says" sounds okay to me. Putting "unlike;y" at the first place emphasizes the unlikeliness, of course.

What is the function of "that" here? With it the headline would sound more natural?

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Unlikely that Covid came from Wuhan lab, WHO says
The long-awaited trip, which was delayed by China, is part of what will be a lengthy process of piecing together the virus’s origin.

Source: abc News Feb.9, 2021 (Updated Feb. 10, 2021)
https://www.nbcnews.com/news/world/who-s-covid-mission-china-give-first-report-n1257105

 

[tzfujimino]

It's unlikely that ...

The "It's" is left out there.

 

[jutfrank]

As tzfujimino correctly points out, the pattern here is: BE + unlikely + that + clause

The that is not normally required in this pattern, but given that the whole phrase is in a highly reduced form (with the omission of subject and copula), it is necessary for intelligibility, because without it a reader would be led to parse unlikely as modifying Covid.