Federal health officials are concerned that a recent uptick in so-called Hib infections in Minnesota infants may signal a comeback of the deadly bacterium as a consequence of a vaccine shortage and the reluctance of some parents to immunize their children.
Minnesota recorded five cases of infection by Haemophilus influenzae Type B last year, the highest number since 1992, including three in November and December. The death of a 7-month-old was the first Hib fatality in a child there since 1991.
In two cases, parents refused to have their child immunized. In a third, they asked to defer vaccination until the child was 5, long after the shots are usually given.
"Parents need to know this disease is still around and that it is very dangerous," Anne Schuchat, head of immunization at the Centers for Disease Control and Prevention, said yesterday.
"I can't emphasize how important it is to use this tool in our toolbox," Ruth Lynfield, Minnesota's state epidemiologist, said of the Hib vaccine, normally given at 2, 4, 6 and 15 months of age.
Hib can cause several types of infection, all of them potentially fatal. Three of the Minnesota children had meningitis, one had pneumonia and one had epiglottitis, an infection of a structure in the back of the throat.
Since the Hib vaccine became widely available in 1990, infections have fallen by 99 percent nationwide. Minnesota used to have 200 to 250 each year in children; now sometimes there are none.
The five recent cases occurred independently, suggesting that the microbe is circulating widely in the population and is not just being passed in a high-risk environment such as a day-care center.
Whether this is happening elsewhere and has just not been noticed is the major unanswered question.
Minnesota traditionally has high vaccination coverage and is not known for having a vocal anti-vaccine community, as is the case in Oregon, Washington state Colorado, among other places. It also has unusually good disease surveillance, which could explain the discovery of the five cases.
"We don't know whether this problem is occurring in other states, but we really want to heighten the awareness of this problem," Schuchat said.
A relative shortage of Hib vaccine may also be contributing.
While two companies make the vaccine in the United States, only one, Sanofi Pasteur, is now supplying the market. The other producer, Merck, recalled its vaccine in December 2007 because of questions about its sterility. The company is not expected to be shipping vaccine again until the middle of this year, a spokeswoman said.
Because of the shortage, physicians have been asked to defer the fourth dose of Hib vaccine, the "booster," unless a child is at high risk for infection because of other illnesses.
Although theoretically there is enough vaccine to provide the first three shots for all American babies, a Minnesota survey suggests that may not be true everywhere. Infants there were nearly 20 percent less likely to have received their three Hib shots than to have had three shots of another vaccine (for diphtheria, tetanus and pertussis) given on the same schedule.
In addition to the three children who were never vaccinated, one of the Minnesota children received three doses but was found to have an immune-deficiency disease that increased risk. The fifth child had two doses.
Lynfield said that overall there appears to be a decline in "herd immunity" to Hib in Minnesota -- the situation in which the few susceptible children are protected by the many immunized ones, who block the microbe from entering the population.
The nation last year saw seven outbreaks of measles in the United States and 140 cases, the largest number since 1996. One occurred in a San Diego charter school where about 35 percent of parents signed vaccine exemptions for their children.
Vaccine refusal in Britain is now so widespread that measles, once eliminated there, is endemic again.