As only few than half the parents took part in the ballot, the vote was declared invalid.

由于只有不到一半的家长参加了投票，所以它被宣布为无效的。

youdao

The second round was required after a U.N.-backed investigation into the vote found widespread fraud and a third of Mr.Karzai's ballots were declared invalid, reversing his outright victory.

VOA: standard.2009.10.28

But monitors noted only a few isolated cases of administrative errors, and none declared the vote invalid.

WSJ: Egyptian Opposition Finds Unity Against Military

If it decides Friday's vote was invalid, Turkey must hold snap general elections.

NPR: Standoff Develops in Turkey Over Moderate Islamist

Those same folk vote in elections: are their voices invalid then?

ECONOMIST: Charlemagne