SELECT zone, DATE_FORMAT(creation_date, '%Y%u') AS date, COUNT(DISTINCT vessel_imo) AS vessel_count FROM vessel_position
WHERE zone IS NOT NULL
AND creation_date >= DATE_SUB(CURDATE(), INTERVAL 12 MONTH)
GROUP BY zone, date;

+----+-------------+-----------------+------------+-------+--------------------+------+---------+------+----------+----------+------------------------------------------+
| id | select_type | table           | partitions | type  | possible_keys      | key  | key_len | ref  | rows     | filtered | Extra                                    |
+----+-------------+-----------------+------------+-------+--------------------+------+---------+------+----------+----------+------------------------------------------+
|  1 | SIMPLE      | vessel_position | NULL       | range | creation_date,zone | zone | 5       | NULL | 21190904 |    50.00 | Using where; Using index; Using filesort |
+----+-------------+-----------------+------------+-------+--------------------+------+---------+------+----------+----------+------------------------------------------+