Hib is Haemophilus influenzae type B. Before a vaccine became available in 1992, some 20,000 U.S. children under age 5 got severe Hib infections every year, resulting in about 1,000 deaths.
Minnesota hadn't had a Hib death since 1991. Now the state is facing it's biggest outbreak since 1992 -- and it may not be just that one state, warns Anne Schuchat, MD, director of the CDC's National Center for Immunization and Respiratory Diseases.
"The situation in Minnesota might be isolated, or it might be the beginning of a trend in other places," Schuchat said at a news conference. "We are working hard to determine which of these stories is the right one."
One of the five Minnesota Hib meningitis cases was in a 5-month-old child too young to have finished its first series of Hib shots. Another case was in a child who got all the shots but who turned out to have an immune deficiency.
The other three cases -- including the death -- were in infants whose parents refused to vaccinate them. Parents of two children objected to vaccines; the parents of the third child were waiting to vaccinate until the child was 5 years old.
"We had a death from a child who was unvaccinated. We want to encourage parents who have delayed or refused vaccination to reconsider," Kristen Ehresmann, RN, MPH, of the Minnesota Department of Health, said at the news conference. "Hib vaccine not only protects your child, but also protects babies who have not completed their primary series or those who have immune compromise."
The CDC is warning all parents of young children to make sure their kids have finished their primary Hib vaccination. Parents who aren't sure are urged to check with their doctors as soon as possible.
"Parents who wondered whether Hib vaccination is really necessary need to know the disease is still around," Schuchat said. "It is a very dangerous disease and we have a vaccine that can protect children. The situation where community protection kept unimmunized kids at low risk of disease does not appear to be holding."
There's been a Hib vaccine shortage since December 2007, when Merck shut down its vaccine manufacturing plant because of possible bacterial contamination. Merck made about half the Hib vaccine used in the U.S. It won't have new vaccine at least until this summer.
Sanofi's Hib vaccine is still available, and there should be enough to cover the basic three-shot series for infants as well as catch-up shots for latecomers. Unlike the two-shot Merck vaccine, the three-dose Sanofi vaccine is given at 2, 4, and 6 months.
There's supposed to be a booster shot at 12-18 months for either vaccine, but the CDC has asked parents to hold off on that shot until the shortage is over (unless their child is at high risk of Hib illness).
Children who have not had their Hib shots and who are at least 1 year old need only one Hib shot, Schuchat says.
Why is there a Hib outbreak now? Minnesota data suggest that the Hib vaccine shortage is playing a role. A quick study shows that 18% of 7-month-old Minnesota kids who got other vaccines did not complete their primary Hib vaccination.
"We interpret this as a shortage of vaccine. Providers did not have the vaccine in their offices," Minnesota state epidemiologist Ruth Lynfield, MD, said at the news conference.
That has probably created a pool of children vulnerable to Hib infections. Before the shortage, widespread Hib vaccination kept infection rates low enough to protect even unvaccinated kids -- a phenomenon called "herd immunity."
But now that protection has ebbed below the level needed to maintain herd immunity, unvaccinated kids pose a threat to kids whose age or immune status make them extremely vulnerable to serious Hib complications.
And Hib can be quite serious. The bug's name, Haemophilus influenza, is confusing. In the days before viruses were discovered, it was thought to be the cause of flu. That's not true. But Hib bacteria can cause pneumonia, severe upper airway infection, and meningitis. Even if not fatal, Hib meningitis can leave children deaf or with severe brain or nerve damage.