Jul 19 2006
A new systematic review suggests that a certain kind of vaccine may help to protect babies and small children from a devastating killer: meningococcal meningitis.
However, this particular vaccine is not approved for use in the United States, and while it may boost immunity, no randomized controlled studies so far have proven its actual clinical effectiveness.
The review looks at serogroup C conjugate meningococcal vaccines (MCC) and their possible role in helping to prevent bacterial meningitis and its complications. Such vaccines are already widely used in Great Britain, Canada and Spain.
"The studies in our review showed that MCC vaccine was highly immunogenic in infants after two and three doses, in toddlers after one and two doses, and in older age groups after one dose," said lead researcher Dr. Lucieni Oliveira Conterno of the Marilia Medical School in São Paulo, Brazil.
The review appears in the current issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.
The review authors analyzed information from 17 randomized clinical studies on antibody responses to MCC vaccines and observational studies.
The MCC vaccine protects against only one "type" of meningitis, called serogroup C. The vaccine has not been approved by the Food and Drug Administration. MPLS (meningococcal polysaccharide) vaccines, by contrast, are approved and already used in the United States and elsewhere.
"In general, higher titers were generated after MCC than after MPLS vaccines," Conterno said. A "titer" is a measurement of antibody levels in a blood sample.
The meningitis vaccine most routinely given in the United States is called "MCV4." This vaccine offers protection from four types of meningitis, including serogroup C. And like the MCC vaccine, it has the additional advantage of being "conjugated" — that is, it uses a carrier protein which tends to enhance the body's immune response to the vaccine.
In the United States, the MCV4 vaccine is normally first given to children at ages 11 to 12 years or when they enter high school. MCV4, unfortunately, does not work well in infants.
Most U.S. doctors do not currently recommend that any meningitis vaccine be routinely administered to babies and small children. It is reserved, rather, for children ages 2 and older at high risk for meningococcal infection, including those without spleens, with serious immune system deficiencies, or those exposed to meningitis.
"The review concluded that if one were to use conjugated vaccine in an attempt to protect against serogroup C in infants, it would likely be effective," said Julia A. McMillan M.D., a professor of pediatrics at Johns Hopkins University School of Medicine. "There is, however, no FDA-approved conjugated vaccine in the U.S. that contains antigen against serogroup C alone."
"About 50 percent of the meningococcal infection that occurs in infants is due to serogroup B meningococcus," added McMillan, a member of the infectious disease committee of the American Academy of Pediatrics. "There is currently no available vaccine, conjugated or not, that protects against serogroup B."
"This review can improve the confidence of using MCC vaccine, based on good evidence about immunogenicity and indirect evidence of clinical efficacy," said Conterno.
But since there were no randomized controlled studies demonstrating the efficacy of the MCC vaccine in the ‘real world' clinical setting, she could only say they might work — not that they actually do.
Meningococcal disease, caused by the bacterium Neisseria meningitidis, is a leading cause of bacterial meningitis and sepsis in the United States. There are an estimated 2,500 to 3,000 U.S. cases per year.
The disease has an overall mortality rate of 13 percent, and can be particularly deadly in infants, because their immune systems are not yet mature enough to fight off the infection as well as teenagers or adults. Antibiotics are used to treat meningitis.
The symptoms and signs of bacterial meningitis include sudden headache, fever, and neck stiffness, sometimes accompanied by nausea, vomiting, sensitivity to light, intense muscle pain and altered mental status. In infants, clinical signs may develop more slowly and may be harder to recognize, but a bulging fontanel (a soft spot on a baby's head) can sometimes be seen.
As the disease progresses it can lead to widespread tissue damage and overwhelming infection of the circulating blood, or what used to be called "blood poisoning."
According to the Centers for Disease Control and Prevention, the manufacturer supplying MCV4 vaccine to the U.S. is experiencing a high-volume demand for the vaccine at present.
"Vaccine is being allocated in both public and private sectors based on estimates of monthly needs as well as available supply," said CDC spokeswoman Lola Russell in a written statement.
With not enough vaccine to go around, medical providers are being asked to defer giving the vaccine to children ages 11 to 12 and to give it instead to adolescents entering high school and college freshmen living in dormitories.
By Joel R. Cooper
http://www.hbns.org
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