REUTERS/Vincent Kessler

Published: Dec 23, 2013 4:22 PM EST

Drugmaker Merck is recalling vials of its HPV vaccine after it says glass may have ended up in the containers.

The Centers for Disease Control and Prevention says it happened during the manufacturing process of the vaccine Gardasil.

The lot was sent out between August and October.

Officials say patients may have mild symptoms, such as swelling at the injection site, but it did not impact the vaccine itself.

Merck is contacting the clinics that received the recalled lot so the company can return those vaccines.