On Thursday, U.S. health officials urged doctors to be more vigilant for suspected cases of invasive Haemophilus influenzae type b (Hib) in young children. Health officials are concerned about meningitis and sepsis, both bloodstream infections caused by Hib.

Last year, Merck & Co Inc recalled their Hib vaccines because of questions over the sterility of their production equipment. At the time, Merck said it planned to resume normal production late this year, but in October, this year, the company announced the vaccines would not be available until the middle of next year.

According to the Centers for Disease Control and Prevention, there has been no significant increase in the incidence of invasive Haemophilus influenzae type b (Hib) in young children since the beginning of the vaccine shortage. The annual rate of invasive Hib disease in children younger than five years was 0.13 per 100,000 during January-October 2008, compared with 0.11 per 100,000 children in 2007, according to the CDC.

But an analysis of a similar situation in England showed that Hib rebound was still possible. CDC epidemiologist Mike Jackson said there is enough vaccine to give children the primary doses at 2, 4, and 6 months of age, but not the booster doses. “We are not worried about sudden increases in Hib disease, but we are worried over time that, not having the booster, we could start to see increases in Hib,”Jackson said. Jackson advised doctors to notify local health departments if they find cases of Hib disease in children and get a clinical specimen for confirmation of the disease.