Merck & Co Inc. on Wednesday voluntarily recalled about 1.2 million doses of its widely used children's vaccines after quality-control checks found production equipment may not have been properly sterilized.

The vaccines protect against Hib disease (Haemophilus influenzae type b), which used to be the leading cause of bacterial meningitis in children less than 5 years old, according to the U.S. Centers for Disease Control and Prevention.

Merck said it recalled 11 lots of PedvaxHIB vaccine and two lots of its Comvax vaccine due to lack of assurance of product sterility. Both of the recalled vaccines protect against Hib and other conditions. Comvax also prevents hepatitis B.

The vaccines were manufactured in West Point, Pennsylvania, and distributed starting in April 2007. All but one lot was distributed in the United States, the company said.

Sterility tests of the vaccine lots subjected to recall did not turn up any contamination, said Merck, which added that the recall does not affect any other vaccines it manufactures.

Children who have received the affected vaccine do not need to be revaccinated because efficacy was not compromised, said Dr. Anne Schuchat, director of the CDC's National Center for Immunization and Respiratory Diseases.