Merck & Co. is recalling about a million doses of a childhood vaccine, after testing showed a sterilization problem in a Pennsylvania factory.

The U.S. company is not aware of any harm to children who received the vaccine, known as Hib, which prevents meningitis and pneumonia. It is a three-dose shot recommended for all children under the age of five and is usually given to infants starting at two months old.

The recall involves 10 lots of Hib vaccine and two lots of a combination vaccine for both Hib and hepatitis B, a Merck spokeswoman said.

She said the company did not find contamination in the vaccine itself, but in the plant where the vaccine is produced in West Point, Pa.

There was no word on Wednesday night of how the recall affects Canada.

Merck, based in Whitehouse Station, N.J., is one of the few drugmakers that produces a significant number of vaccines.

While the company took a black eye with its September 2004 withdrawal of the painkiller Vioxx due to increased risk of heart attacks and strokes, the company has been performing well recently. On Tuesday, it gave an upbeat assessment in its annual briefing for analysts.

Five weeks ago, Merck reached a deal to settle up to 50,000 Vioxx lawsuits for $4.85 billion US, an amount expected to save the company millions in trial costs.

Its stock price has more than recovered from its post-Vioxx slump, a two-year-old restructuring plan is going well and profits are up. For example, Merck posted a 62 per cent increase in its third-quarter profit as revenues jumped by double digits.