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: Because measles causes an estimated 2 million deaths per year among children in developing countries, including a substantial proportion of infants less than nine months old - the age at which vaccination is recommended - there has been interest in using different strains of vaccine and higher doses to achieve immunization of younger infants.

We conducted a randomized trial of three different doses of Edmonston-Zagreb and of Schwarz measles vaccines in infants to evaluate the effect of the strain and dose of vaccine on the serologic response and acute adverse reactions to vaccination. Six-month-old infants received a standard, medium, or high dose of one of the vaccines, and nine-month-old infants received a standard dose. Antibody levels were measured before and after vaccination, by means of a plaque-reduction neutralization assay, in 1061 six-month-olds and 299 nine-month-olds.

Edmonston-Zagreb vaccine produced higher rates of seroconversion and seropositivity than comparable doses of Schwarz vaccine. Among the six-month-old infants, the seroconversion rate 18 weeks after vaccination with the standard dose of Edmonston-Zagreb vaccine was 92 percent, that with the medium dose was 96 to 97 percent, and that with the high dose was 98 percent; the rates for the corresponding doses of Schwarz vaccine were 66 percent, 76 percent, and 91 percent, respectively. Higher seroconversion rates were observed with an increase in the dose of either Edmonston-Zagreb (P<0.01) or Schwarz (P<0.001) vaccine. The seroconversion rates produced by high and medium doses of Edmonston-Zagreb vaccine in six-month-olds were equal to or significantly higher than the rate produced by a standard dose of Schwarz vaccine in nine-month-olds (87 percent). Clinical adverse reactions were not associated with the strain or dose of a vaccine.

We conclude that Edmonston-Zagreb vaccine is more immunogenic than Schwarz vaccine in infants and can induce effective immunization against measles at six months of age. (N Engl J Med 1990; 322:580-7.)

: MEASLES remains a major cause of childhood morbidity and mortality in developing countries. It is estimated that more than 2 million children die of measles each year.1 Measles also causes blindness, diarrhea, and malnutrition in many children who survive the acute illness. Live attenuated measles vaccines, available since the 1960s, are an effective means of reducing the incidence of measles in many countries. The administration of these vaccines results in seroconversion rates of over 90 percent in older infants; however, transplacentally acquired maternal antibody interferes with the successful immunization of young infants.2 3 4 Therefore, the World Health Organization has recommended that [horizontal ellipsis]

Owned, published, and (C) copyrighted, 1990, by the MASSACHUSETTS MEDICAL SOCIETY