Índice espacial do MySQL não utilizado

mysql> DROP TABLE IF EXISTS `geoDirections`;
Query OK, 0 rows affected (0.00 sec)

mysql> CREATE TABLE `geoDirections` (
    ->    `id` INT(11) NOT NULL,
    ->    `from` POINT NOT NULL,
    ->    `to` POINT NOT NULL
    -> ) ENGINE=InnoDB;
Query OK, 0 rows affected (0.01 sec)

mysql> ALTER TABLE `geoDirections`
    ->     ADD PRIMARY KEY (`id`),
    ->     ADD SPATIAL INDEX (`from`),
    ->     ADD SPATIAL INDEX (`to`);
Query OK, 0 rows affected (0.00 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> EXPLAIN SELECT `g`.`from`
    -> FROM `geoDirections` `g`
    -> WHERE
    ->       ST_Contains(ST_Buffer(
    ->           ST_GeomFromText('POINT(-2.00751 48.6547)', 4326), (0.00001 * 20)), `g`.`from`) 
    ->       AND
    ->       ST_Contains(ST_Buffer(
    ->           ST_GeomFromText('POINT(-2.05757 48.6338)', 4326), (0.00001 * 20)), `g`.`to`)\G
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: g
   partitions: NULL
         type: ALL
possible_keys: from,to
          key: NULL
      key_len: NULL
          ref: NULL
         rows: 1
     filtered: 100.00
        Extra: Using where
1 row in set, 1 warning (0.00 sec)