PDO variable not capturing/passing value - pdo

Question

This code works but it is one change short of proper PDO--I would need to change " $user_ID " in the where clause to " :user_ID ".
HOWEVER, when I do that, the code doesn't update the contributions by 3 (which is the goal of the code). But it does work and update contributions as long as I don't change $user_ID to :user_ID.
Can anyone see why and what I'm doing wrong from this?
$yesupdate = "UPDATE points SET contributions = contributions + 3 WHERE ID
= $user_ID";
$stmt4 = $dbh->prepare($yesupdate);
$stmt4->bindParam(':user_ID', $user_ID, PDO::PARAM_INT);
$stmt4->bindParam(':WID', $yes_WID, PDO::PARAM_INT);
$stmt4->bindParam(':approved', $e = Y, PDO::PARAM_STR);
$stmt4->bindParam(':position', $row2[0]['position'], PDO::PARAM_INT);
$stmt4->execute();
FYI, the above code is a second query that follows the below query:
$yesupdate = "UPDATE writing SET approved = :approved, position = :position
WHERE WID = :WID";
$stmt2 = $dbh->prepare($yesupdate);
$stmt2->bindParam(':WID', $yes_WID, PDO::PARAM_INT);
$stmt2->bindParam(':approved', $e = Y, PDO::PARAM_STR);
$stmt2->bindParam(':position', $row2[0]['position'], PDO::PARAM_INT);
$stmt2->execute();