Herd immunity for Hib dropping

After recommending deferring some Hib doses due to a shortage of the vaccine in 2007, the Centers for Disease Control and Prevention (CDC) recorded five new cases of invasive Hib disease in Minnesota.

The case illustrates the unusual world of vaccines, where best practices are sometimes changed based on real-world issues such as supply. In this case, a possible contamination at a Merck facility prompted a recall of a million doses of Hib: it and Schering-Plough are the only two makers of Hib (haemophilus influenzae type b) vaccines.

After the recall, CDC halted its recommendation for a booster shot of the Hib vaccine at 12 to 15 months. It wanted there to be enough Hib vaccine for the more important 2-, 4- and 6-month vaccine series.

One of the five Minnesota children who caught Hib died from meningitis. Most had not been immunized at all, or received partial immunizations. The risk of loss of herd immunity spurred CDC to stress the importance of the initial three shots. When vaccine supply is more robust, it will presumably re-recommend the 12- to 15-month follow-up shot as well.