It was found that fewer than one in a hundred people had been vaccinated against endemic diseases.

Literal

Endemic-disease [target-に対する] vaccination [object-を] received [topic-は] hundred-people [scope-中] one-person [also-にも] not-reach [quotative-ということが] was-found.

A complex statistical sentence. 風土病 means 'endemic disease.' 一〇〇人中一人にも満たない means 'less than one person in a hundred.' 見出された is the passive of 見出す (to discover/find). Dense, formal writing.