The word "this" is used to identify a specific person or thing close at hand or being referred to (in this case, a specific influenza lineage).

If the word "the" were used instead, the headline wouldn't make sense.

Personally i think using "An" would be better than "this" or nothing at all, but i also think this entire thread is very nitpicky.

Good point, the title of the article is: "Influenza lineage extinction during the COVID-19 pandemic?", I don't know how the HN headline came to be ("This influenza lineage may have become extinct"), but it does seem like a very very light form of clickbait.

It's a quote from the abstract. I found "influenza lineage extinction" difficult to parse, but the abstract expands it into clear English.

>"In particular, the B/Yamagata lineage has not been isolated from April 2020 to August 2021, suggesting that this influenza lineage may have become extinct,"

So I'm not the only one who notices this.

The unnecessary this prefix strikes me as a sort of clickbait-adjacent red flag. I'm fairly sure it wasn't anywhere near this common 10 years ago.

Often with a short follow-on sentence in the format:

This article is clickbait. Here's why.