3 years

Window of effectiveness of the whooping cough vaccine, which is shorter than expected, according to preliminary data presented Monday at a medical conference in Chicago. The researchers looked at whooping cough cases in California, where the disease spiked last year and where vaccination has become a divisive issue. The study involving 15,000 kids in Marin County found that those who had been fully vaccinated three or more years previously were up to 20 times more likely to become infected than kids who had been more recently vaccinated; the largest number of cases was in kids aged 8 to 12. The whooping cough vaccine is given in five doses — at 2 months, 4 months, 6 months; between 15 and 18 months; and at 5 years. The booster is given at 12 years. The new findings are likely to stir debate over whether the booster should be given sooner. [via AP]