Serological response to cholera revaccination in a semi-closed community in Calcutta.

Serological response to cholera revaccination has been studied in a semi-closed community consisting of individuals mostly in the 2-20-years age-group. The subjects had been inoculated against cholera every year at the beginning of the local epidemic season. Pre- and post-vaccination sera were obtained from 29 subjects inoculated with cholera vaccine (test group) and 28 from subjects inoculated with TAB vaccine (control group). These sera were tested for vibriocidal and agglutination titres. The geometrical means of the vibriocidal and agglutination titres of the post-vaccination sera in the test group rose by 490% and 463% respectively. This booster effect was observed mostly in individuals in the 2-14-years age-group, who had low titres (vibriocidal

Controlled field trial of the effectiveness of cholera and cholera El Tor vaccines in Calcutta.

To assess the effectiveness of cholera vaccines, 2 controlled field trials were made in Calcutta-an endemic area-during 1964 and 1965. Three Indian vaccines of which 1 was grown on casein hydrolysate and 2 on agar, a freeze-dried vaccine from the Walter Reed Army Institute of Research (WRAIR), Washington, D.C., and an El Tor vaccine from the Philippines were used, with typhoid-paratyphoid (TAB) vaccine as a control. The 210 112 volunteers were vaccinated subcutaneously with a single dose of one of the vaccines.In the 1964 trial, the number of bacteriologically confirmed cases was not enough to show statistically significant differences in incidence between the 5 vaccine groups and the control group. However, the WRAIR freeze-dried vaccine protected about 40% of the vaccinees for 6 months after vaccination, although the efficacy was higher (57%) during the first 3 months than during the subsequent 3 months (28%). Agar-grown vaccine, produced by the Central Research Institute, Kasauli, was 37% efficacious.In the 1965 trial, owing to the small number of cases in the study area, the Kasauli vaccine was the only one to show statistically significant protection (40%).

Cholera carrier studies in Calcutta in 1966-67.

Cholera carrier studies have been in progress in Calcutta since April 1966, in areas of high endemicity with a population of about 13 000. Carriers are traced through periodic examinations of samples from latrines, users of vibrio-positive latrines, contacts of cases of cholera and apparently healthy persons.The latrine survey showed that 46.2% of the latrines were infected, and brought 54 carriers to light; the over-all carrier rate in the study area was estimated as 1.3%. The carrier rate among household and family contacts of hospital cases of cholera was 1.6%. None of the contacts of 9 persons with choleraic diarrhoea was positive. Vibrios were also isolated from water and flies near positive latrines.The results indicate that carriers can occur even in the absence of overt disease, that infection persists in many households, and that carriers may transmit the infection.