A vaccine against a common type of bacterial meningitis protected older children and young adults during a 1995 outbreak in Texas, according to a report in tomorrow's Journal of the American Medical Association. But experts caution that because the vaccine is expensive and its effectiveness wears off, it should be used only to contain rather than prevent major outbreaks.
The bacterium Neisseria meningitidis infects roughly 2600 Americans each year and kills between 10% and 15%. Symptoms include a stiff neck, severe headache, and vomiting, and, in the late stages, delirium and convulsions. It can kill an otherwise healthy person within 24 hours. Since 1991, the number of outbreaks of a strain called N. meningitidis subgroup C--the most common cause of outbreaks--has doubled, raising alarm among public health officials. But no one knew how effective the current vaccine was.
To evaluate the vaccine, Bradley Perkins and other epidemiologists from the Centers for Disease Control and Prevention (CDC) in Atlanta confirmed and tracked an outbreak in Gregg County, Texas, over 19 months. The Texas Department of Health had conducted a countywide vaccination campaign among residents aged 2 to 10 and then expanded it to include up to age 29 as additional cases were reported. In all, some 36,000 residents--about one-third of the population--were vaccinated at 30 clinics. The CDC team compared Gregg County residents who were vaccinated with those who weren't, matching patients and controls for several factors, such as age and neighborhood. The vaccine was about 85% effective in the 2- to 29-year-old group and 93% effective among 2- to 5-year-olds.
For the vaccine to be used most effectively, it will be critical to determine what "really constitutes an outbreak," says Michael Osterholm, an epidemiologist with the Minnesota Department of Public Health. Because the current vaccine does not protect children younger than 2 years--and lasts only a few years for everyone--expensive mass immunizations should be ordered only when outbreaks are verified, he says.