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Studies on Trachoma

V. Clinical Observations in a Field Trial of Bivalent Trachoma Vaccine at Three Dosage Levels in Saudi Arabia^*

1. Bivalent trachoma vaccines, inactivated with formalin, were given to 2,117 children in a controlled study in the Eastern Province of Saudi Arabia. Three dosage levels were employed. Subjects were recalled for examination at 6 month intervals for up to 2 years.

2. The smallest amount of trachoma antigens, 0.25 arbitrary vaccine units, emulsified in adjuvant and given as a single injection, produced no observable effect on attack rates of clinical trachoma. The intermediate amount, an aqueous vaccine administered in 2 primary injections containing a total of approximately 0.4 arbitrary vaccine units, was followed by a lower attack rate in vaccinees than in controls, the difference being statistically significant at the 6 month examination. Six months later, although there continued to be less active trachoma in test than in control groups, statistical significance was lacking whether the vaccinees received boosters or not.

3. The largest amount of trachoma antigen, an aqueous vaccine containing 4.0 arbitrary vaccine units in 2 primary injections, was followed by a higher attack rate in the test group than in the controls at the end of 6 months; thereafter differences in attack rate diminished progressively to values less than those required for statistical significance.

^* This study was supported by the Arabian American Oil Company, and grants to the Harvard School of Public Health from the National Institutes of Health (General Research Support Grant, FR-5446-04, and the National Institute of Allergy and Infectious Diseases, AI-06251-02).