Cholera incidence in a population offered cholera vaccination: comparison of cooperative and uncooperative groups

From May 1964 to December 1965, a controlled field trial of the effectiveness of cholera and cholera El Tor vaccines was conducted in Negros Occidental, Philippines. Some people did not volunteer for vaccination, and of those who did some received cholera vaccine and others a control (typhoid) vaccine. After analysing he incidence of cholera among these three groups it was found that the morbidity and mortality rates were significantly higher in the unvaccinated group than in either the control vaccine group or the cholera vaccine group. This would indicate that the unvaccinated group is basically different from the vaccinated control group. The clinical course of the disease was the same whether the patient had been vaccinated or not. The reasons for non-vaccination were investigated and should be taken into account by public health agencies when immunization programmes are being planned.