Matching search strings in web crawler query tester

Hello,

New to elasticsearch.
I've got a elastic cluster, three nodes.
A web crawler has been configured to crawl a domain which seems to be working fine.
I want to configure a curation that queries for all the occurrences of the string "vaccin"

When i enter a query like "vacci", i get results. ('vaccin', 'vaccins', 'vaccination' are all amongst the returned result.)

However, when i enter a query like "vaccins" or "vaccin" , i get zero matches. "no matching content found" but there is absolutely matching content. (the 'vacci' search returns it)

What am i doing wrong or what did i not understand ?