Controlled field trial with dried sorbed paratyphoid B and typhoid vaccines.

In 1968-70 a field trial was arranged in the USSR to evaluate the effectiveness of dried sorbed paratyphoid B and typhoid vaccines when administered in two doses separated by an interval of 20-30 days.TWO GROUPS OF SCHOOLCHILDREN WERE UNDER OBSERVATION: a group inoculated with paratyphoid B vaccine (75 805 children) and a group inoculated with typhoid vaccine (76 314 children). The persons who were inoculated with the paratyphoid B vaccine formed the control group used in evaluating the effectiveness of the typhoid vaccine, and those inoculated with the typhoid vaccine formed the control group for the evaluation of the paratyphoid vaccine.Two doses of dried sorbed paratyphoid B vaccine made from Salmonella paratyphi B, strain No. 42, containing 5 x 10(8) microbial cells per injection, protected about 70% of those inoculated. Two doses of dried sorbed typhoid vaccine made from S. typhi, strain Ty 2 4446, also with 5 x 10(8) cells per injection, protected about 80% of those inoculated.At least 21 months of protection (the period of observation) were obtained following immunization with dried sorbed preparations made from heat-killed aerated broth cultures.Both types of vaccine produced the same frequency and intensity of general and local reactions; these were moderate. The general and local reactions to a second injection were substantially less marked than those to the first.

A controlled field trial to evaluate the protective capacity of a single dose of acetone-killed agar-grown and heat-killed broth-grown typhoid vaccines.

In a strictly controlled field trial among schoolchildren a study was made of the protective capacity of single doses of 2 typhoid vaccines: a heat-killed broth-grown sorbed dried vaccine made in the USSR (vaccine G-66) and an acetone-killed agar-grown dried vaccine (vaccine K-66) made in Yugoslavia. The latter vaccine was supplied by the World Health Organization.A single dose of these preparations exerted a statistically significant protective effect during the first 10 months of observation. The protection afforded by the acetone-killed and heat-killed sorbed vaccines was similar in duration and intensity to that resulting from single doses of other types of typhoid vaccines that had been evaluated earlier in the USSR. The data obtained confirm once again that successful immunization against typhoid is possible with a single dose of vaccine.The absence of any substantial difference in morbidity between the groups concerned indicates that the heat-killed broth-grown and acetone-killed agar-grown vaccines exert a roughly similar protective effect.

Controlled field trials of paratyphoid B vaccine and evaluation of the effectiveness of a single administration of typhoid vaccine.

In 1963 and 1964 field trials were organized in the USSR for the purpose of evaluating the effectiveness of paratyphoid B vaccine. An opportunity was thereby afforded to assess the effectiveness of a single administration of typhoid vaccine, used as the preparation administered to the paratyphoid control group of 89 046 persons. Similarly, the control group used for assessing the effectiveness of the typhoid vaccine was the group of 86 620 persons inoculated with the paratyphoid vaccine.It was established that it is, in principle, possible to immunize people effectively against paratyphoid B by administering heat-killed paratyphoid B vaccine prepared from an aerated broth culture. It was found that the protective effect of the vaccine depends upon the size of the dose and the number of times it is administered. A protective effect was produced when a dose of 6 x 10(8) organisms was administered to persons from 7 to 16 years of age. Two inoculations of the paratyphoid B vaccine ensured protection over the 30 months that the observations lasted, whereas a single administration only conferred protection for up to one year.It was also confirmed that it is possible to obtain a protective effect with a single administration of a heat-killed typhoid vaccine prepared from an aerated broth culture. A single administration of the typhoid vaccine had a less marked protective effect (index of effectiveness 58%) than 2 administrations, a fall in the level of the protection conferred occurring during the year after immunization. The frequency and intensity of general and local reactions were identical for equal doses of typhoid and paratyphoid B vaccine.