By ATLANTA - Teens should get a booster dose of the vaccine for bacterial meningitis because a single shot doesn't work as long as expected, a federal advisory panel said yesterday.. The vaccine was initially aimed at high school and college students because the disease is more dangerous for adolescents and can easily spread in crowded conditions, like dorm rooms.. Three years ago, the Advisory Committee on Immunization Practices said the vaccine should be offered to children ages 11 and 12. They believed the shot was effective for at least 10 years.. But the panel was told Wednesday that studies show the vaccine works for less than five years. The 6-5 vote for a booster at age 16 was unusually close for the panel.. The committee also recommended that people 65 and older who are around infants get vaccinated against whooping cough to help prevent its spread. Whooping cough vaccine is not currently recommended for the elderly.. The vaccine group provides advice to the Centers for Disease Control and Prevention. The CDC and the U.S. Department of Health and Human Services usually adopt the panel's recommendations.. However, the meningitis booster shot recommendation may not be adopted quite so easily. A Food and Drug Administration official, Norman Baylor, said more studies about the safety and effectiveness of a second dose of the vaccine are needed.. Some wondered if it was even necessary to make such a decision. Cases of bacterial meningitis are at historic lows.