Two Measles Doses are Better Than One
ABSTRACT & COMMENTARY
Synopsis: Measles vaccine effectiveness was evaluated in a school outbreak of measles in Colorado. Vaccine effectiveness was 92% for one dose and 100% for two doses. The two-dose strategy is important in preventing measles outbreaks.
Source: Vitek CR, et al. Increased protections during a measles outbreak of children previously vaccinated with a second dose of measles-mumps-rubella vaccine. Pediatr Infect Dis J 1999;18:620-623.
An outbreak of 62 confirmed cases of measles in 1994 in Mesa County, Colo., was investigated to evaluate vaccine effectiveness. The attack rate in unvaccinated children (7/16, 44%) was higher than those who had had one dose (10/320, 3%) or two doses of vaccine (0/289, 0%). Two doses of measles vaccines provided 100% protection, compared to 92% for one dose (P = 0.003).
Comment by Hal B. Jenson, MD, FAAP
Although we may now be approaching the elimination of measles in the United States, between 1984 and 1988, an average of 3700 cases of measles were reported annually, with a sharp rise in 1989 that continued in 1990 when 27,786 cases of measles were reported. In 1989, the American Academy of Pediatrics and the Advisory Committee on Immunization Practices (ACIP) of the CDC recommended that a second measles dose be given (as MMR). The current recommendations are for the first dose at 12-15 months of age, and the second dose routinely at 4-6 years of age, although the second dose can be administered at any visit if at least one month has elapsed since receipt of the first dose and both doses are administered at or after 12 months of age. Children who have not previously received the first dose should complete the schedule no later than the routine visit at 11-12 years of age. Since this recommendation, the annual number of cases of measles in the United States has dropped below 100, suggesting, but not proving, that this policy has been effective. The age distribution of children with measles in this outbreak was interesting. The age groups with cases included young children who had not received two doses of measles vaccine, and older children (15-18 years of age) beyond statutory requirements for two doses of measles vaccine. There were no cases of measles among children 12-14 years of age, for whom state law had required two doses of measles vaccine. This suggests that we should be diligent to make sure all children receive two doses, and don’t assume that age is protective.
This study is the first that evaluates the effectiveness of the two-dose measles policy in an outbreak, which is the setting in which we are most likely to encounter measles in the United States today. The results convincingly demonstrate the importance and the effectiveness of the second dose in preventing measles, and substantiate the current recommendations for a second dose of measles vaccine for all children. (Dr. Jenson is Chief, Pediatric Infectious Diseases, University of Texas Health Science Center, San Antonio, TX.)
True statements about measles vaccination include all of the following except:
a. the first dose is recommended at 12-15 months of age.
b. the second dose is recommended at 4-6 years of age.
c. clinical measles occurs largely in children who have received only one dose.
d. a second dose is not recommended for children older than 15 years of age.
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