Why does Merck write Jiadaxiu 9?

jiadaxiu 9 is a vaccine developed by Merck. Merck wrote Jiadaxiu 9 because Jiadaxiu 9 is a vaccine developed by Merck, which is a super-nine-valent vaccine with five subtypes of viruses, namely 31, 33, 45, 52 and 58, added to the original tetravalent vaccine.