PHP PDO prepared statement with IN [closed]

Question

Here's my code:

<?php
$db = new PDO('mysql:dbname=dbname;host=host', 'user', 'pass');

$ne = explode(',', $_GET['ne']);
$sw = explode(',', $_GET['sw']);

$shape = "Polygon((
  $sw[0] $sw[1],
  $ne[0] $sw[1],
  $ne[0] $ne[1],
  $sw[0] $ne[1],
  $sw[0] $sw[1]
))";

$sql_where = '';
if (strlen($_GET['exclude'])) {
  $exclude = array_map('intval', explode(',', $_GET['exclude']));
  if (count($exclude)) {
    $exclude = implode(',', $exclude);
    $sql_where = "AND countyfp NOT IN ($exclude)";
  }
}

$q = $db->prepare("
  SELECT
    name,
    countyfp AS fips,
    ST_AsGeoJson(SHAPE) AS shape
  FROM county_shapes
  WHERE MBRIntersects(ST_GeomFromText(:shape, 4269), SHAPE)
    $sql_where
");

$q->execute(compact('shape'));

$result = [];
while ($row = $q->fetch(PDO::FETCH_ASSOC)) {
  $row['shape'] = json_decode($row['shape']);
  $result[] = $row;
}

echo json_encode($result);

Can it be improved upon? I don't like the idea of dumping a variable into an SQL query but I'm not sure what other options I have.

Here's the schema:

CREATE TABLE `county_shapes` (
  `OGR_FID` int NOT NULL AUTO_INCREMENT,
  `SHAPE` geometry NOT NULL /*!80003 SRID 4269 */,
  `statefp` varchar(2) DEFAULT NULL,
  `countyfp` varchar(3) DEFAULT NULL,
  `countyns` varchar(8) DEFAULT NULL,
  `geoid` varchar(5) DEFAULT NULL,
  `name` varchar(100) DEFAULT NULL,
  `namelsad` varchar(100) DEFAULT NULL,
  `lsad` varchar(2) DEFAULT NULL,
  `classfp` varchar(2) DEFAULT NULL,
  `mtfcc` varchar(5) DEFAULT NULL,
  `csafp` varchar(3) DEFAULT NULL,
  `cbsafp` varchar(5) DEFAULT NULL,
  `metdivfp` varchar(5) DEFAULT NULL,
  `funcstat` varchar(1) DEFAULT NULL,
  `aland` decimal(14,0) DEFAULT NULL,
  `awater` decimal(14,0) DEFAULT NULL,
  `intptlat` varchar(11) DEFAULT NULL,
  `intptlon` varchar(12) DEFAULT NULL,
  PRIMARY KEY `OGR_FID` (`OGR_FID`),
  SPATIAL KEY `SHAPE` (`SHAPE`)
) ENGINE=InnoDB;

The server is MySQL 8.0.28.