Cholera vaccine field trials in east Pakistan. 2. Effectiveness in the field.

A cholera-vaccine field trial in a rural area of East Pakistan where cholera is highly endemic has indicated that a high-potency whole-cell vaccine can provide significant protection against disease due to Vibrio cholerae for at least 18 months. This vaccine gave more than 70% protection during the first cholera season after vaccination. In the second cholera season after the administration of a single dose of vaccine, protection fell in those under 5 years of age, while continuing at significantly effective levels in older persons.Purified Ogawa antigen (lipopolysaccharide) afforded significant protection to adults against disease due to the heterologous Inaba serotype, but only protected children against milder diarrhoeas.The effect of cholera vaccine on the incidence of infections among family contacts of cholera patients was variable. Vaccine had no effect on the proportion of asymptomatic infections.Diarrhoeal disease associated with V. cholerae occurred predominantly among children, while protection was most marked among adults. Adverse reactions were practically restricted to the adults, suggesting that children will not only tolerate a larger dose, but actually require a larger dose for maximum protection against infection.