John B. Robbins

The Efficacy of a Salmonella typhi Vi Conjugate Vaccine in Two-to-Five-Year-Old Children

BACKGROUND Typhoid fever is common in developing countries. The licensed typhoid vaccines confer only about 70 percent immunity, do not protect young children, and are not used for routine vaccination. A newly devised conjugate of the capsular polysaccharide of Salmonella typhi, Vi, bound to nontoxic recombinant Pseudomonas aeruginosa exotoxin A (rEPA), has enhanced immunogenicity in adults and in children 5 to 14 years old and has elicited a booster response in children 2 to 4 years old. METHODS In a double-blind, randomized trial, we evaluated the safety, immunogenicity, and efficacy of the Vi-rEPA vaccine in children two to five years old in 16 communes in Dong Thap Province, Vietnam. Each of the 11,091 children received two injections six weeks apart of either Vi-rEPA or a saline placebo. Cases of typhoid, diagnosed by the isolation of S. typhi from blood cultures after 3 or more days of fever (a temperature of 37.5 degrees C or higher), were identified by active surveillance over a period of 27 months. We estimated efficacy by comparing the attack rate of typhoid in the vaccine group with that in the placebo group. RESULTS S. typhi was isolated from 4 of the 5525 children who were fully vaccinated with Vi-rEPA and from 47 of the 5566 children who received both injections of placebo (efficacy, 91.5 percent; 95 percent confidence interval, 77.1 to 96.6; P<0.001). Among the 771 children who received only one injection, there was 1 case of typhoid in the vaccine group and 8 cases in the placebo group. Cases were distributed evenly among all age groups and throughout the study period. No serious adverse reactions were observed. In all 36 children studied four weeks after the second injection of the vaccine, levels of serum IgG Vi antibodies had increased by a factor of 10 or more. CONCLUSIONS The Vi-rEPA conjugate typhoid vaccine is safe and immunogenic and has more than 90 percent efficacy in children two to five years old. The antibody responses and the efficacy suggest that this vaccine should be at least as protective in persons who are more than five years old.

Escherichia coli K1 Capsular Polysaccharide Associated with Neonatal Meningitis

Abstract Examination of 77 strains of Escherichia coli from the cerebrospinal fluid of neonates with meningitis revealed 65 (84 per cent) with the capsular (K1) polysaccharide. The Esch. coli K1 ca...

Prevention of typhoid fever in Nepal with the Vi capsular polysaccharide of Salmonella typhi. A preliminary report.

We conducted a pilot study followed by a large clinical trial in Nepal of the use of the capsular polysaccharide of Salmonella typhi (Vi) as a vaccine to prevent typhoid fever. In the pilot study, involving 274 Nepalese, there were no significant side effects of the Vi vaccine; about 75 percent responded with a rise in serum antibodies of fourfold or more. In the clinical trial, residents of five villages were given intramuscular injections of either Vi or, as a control, pneumococcus vaccine dispensed in coded, randomly arranged, single-dose syringes. There were 6907 participants, of whom 6438 were members of the target population (5 to 44 years of age); each was visited every two days. Those with temperatures of 37.8 degrees C or higher for three consecutive days were examined and asked to give blood for culture. Typhoid was diagnosed as either blood culture-positive or clinically suspected on the basis of bradycardia, splenomegaly, and fever, with a negative blood culture. Seventeen months after vaccination, the codes were broken for the 71 patients meeting the criteria for either culture-positive or clinically suspected typhoid. The attack rate of typhoid was 16.2 per 1000 among the controls and 4.1 per 1000 among those immunized with Vi (P less than 0.00001). The efficacy of Vi was 72 percent in the culture-positive cases, 80 percent in the clinically suspected cases, and 75 percent in the two groups combined. These data provide evidence that Vi antibodies confer protection against typhoid. Surveillance continues to determine the duration of Vi-induced immunity.

A placebo-controlled trial of a pertussis-toxoid vaccine.

BACKGROUND Although many whole-cell vaccines have been effective in preventing pertussis, these vaccines are difficult to standardize and can produce side effects. In Sweden, pertussis became endemic during the 1970s despite vaccination. Because of its limited efficacy, the Swedish-made whole-cell vaccine was withdrawn in 1979. METHODS To evaluate the efficacy of an acellular vaccine consisting of pertussis toxin inactivated by hydrogen peroxide (pertussis toxoid), we conducted a randomized, double-blind, placebo-controlled trial in Sweden. Infants were vaccinated with either diphtheria and tetanus toxoids alone (DT toxoids, 1726 infants) or diphtheria, tetanus, and pertussis toxoids (DTP toxoids, 1724 infants) at 3, 5, and 12 months of age. RESULTS There were no serious reactions. With the pertussis vaccine there were slightly more local reactions than with the DT toxoids alone, but the rates of postvaccination fever were the same. The main period of surveillance, which began 30 days after the third vaccination, continued for a median of 17.5 months. There were 312 cases of pertussis (72 in the DTP-toxoids group and 240 in the DT-toxoids group) that met the clinical criterion (paroxysmal cough lasting > or = 21 days) and laboratory criteria for pertussis as defined by the World Health Organization. The efficacy of this acellular vaccine was 71 percent (95 percent confidence interval, 63 to 78 percent). The recipients of DTP toxoids who had pertussis had cough of shorter duration than the recipients of DT toxoids, and fewer had whooping and vomiting. The vaccine efficacy after two doses was 55 percent (95 percent confidence interval, 12 to 78 percent), on the basis of 14 cases in the DTP-toxoids group and 31 in the DT-toxoids group that met the definition of the World Health Organization. CONCLUSIONS A pharmacologically inert, acellular pertussis-toxoid vaccine that is easily standardized is safe and confers substantial protection against pertussis.

Quantitative Measurement of “Natural” and Immunization-induced Haemophilus influenzas type b Capsular Polysaccharide Antibodies

Extract: Haemophilus influenzae type b antibodies were measured quantitatively in normal and immunized humans and in commercially available pooled immunoglobulin. A “protective” serum level was estimated to be 0.06 to 0.1

Immunogenicity, efficacy and serological correlate of protection of Salmonella typhi Vi capsular polysaccharide vaccine three years after immunization

mUg antibody/ml based upon the anti-type b concentration in normal adult sera and pooled immunoglobulin. An age-related difference characterized the adult and infant serum antibody response to injection of the purified type b capsular polysaccharide. The adults responded with higher and sustained antibody levels than the infants and children. An immunized infant reacted with type b antibody formation after nasopharyngeal carriage of H. influenzae type b and two infants reacted with type b antibodies after enteric carriage of Escherichia coli with a cross-reacting antigen.Speculation: Qualitative and quantitative differences characterize the adult versus the infant re-response to the capsular polysaccharide of H. influenzae type b. This age-related difference in the serum anti-type b antibody response may be due to the development of differentiated cells induced by whole bacteria, either as H. influenzae type b or by other organisms with cross-reacting antigens. The “protective” level of serum anti-type b antibodies, estimated by two methods, was achieved by immunization of infants, which suggests that this procedure may confer protective immunity.

Double-blind vaccine-controlled randomised efficacy trial of an investigational Shigella sonnei conjugate vaccine in young adults

The protective efficacy and immunogenicity of Vi capsular polysaccharide vaccine against typhoid fever was measured 3 years after its administration in a double-blind randomized trial. Vaccine efficacy was not significantly different during each year of the trial and was 55% (95% CI: 30-71%) over the 3 year period. In a case-control study at 3 years after vaccination, recipients of Vi had higher levels of Vi antibodies than controls, as measured by radio-immunoassay (GMT 1.28 vs 0.76 microgram ml-1, P = 0.0004) and by passive haemagglutination assay (GMT 10.46 vs 3.52, P = 0.0001). The serological correlate of protection has been estimated using the relative risks of typhoid fever in the 2 groups and the relative ratio of antibody levels. The estimated protective level is 1 microgram ml-1 suggesting that at a mean age of 9 years, 64% of vaccinates and 40% of controls had protective antibody against typhoid fever in this endemic area.

Poly(γ-d-glutamic acid) protein conjugates induce IgG antibodies in mice to the capsule of Bacillus anthracis: A potential addition to the anthrax vaccine

BACKGROUND The aim of this double-blind randomised vaccine-controlled trial was to assess the efficacy of a conjugate vaccine composed of Shigella sonnei O-specific polysaccharide bound to Pseudomonas aeruginosa recombinant exoprotein A (S sonnei-rEPA) and of an oral, live-attenuated Escherichia coli/S flexneri 2a (EcSf2a-2) hybrid vaccine among military recruits in Israel at high risk of exposure to Shigella spp. We report here our preliminary findings on the efficacy of S sonnei-rEPA; we have not documented sufficient cases to assess the efficacy of EcSf2a-2. METHODS Between April, 1993, and August, 1994, male Israeli Military recruits aged 18-22 years were asked to take part in our study. We enrolled 1446 soldiers from seven separate field sites (groups A-G). Soldiers were randomly allocated one injection of S sonnei-rEPA and four doses of oral placebo (n = 576), four oral doses of EcSf2a-2 and one injection of saline placebo (n = 580), or one injection of meningococcal tetravalent control vaccine and four doses of oral placebo (n = 290). Because there were no cases of S flexneri 2a, the EcSf2a-2 and meningococcal vaccines were the control group. We defined S sonnei shigellosis as diarrhoea with a positive faecal culture for S sonnei. Each group of soldiers was followed up for 2.5-7.0 months. The primary endpoint was protective efficacy of S sonnei-rEPA against S sonnei shigellosis. FINDINGS Cases of culture-proven S sonnei shigellosis occurred in four groups of soldiers (groups A-D), which comprised 787 volunteers (312 received S sonnei-rEPA, 316 received EcSf2a-2, and 159 received meningococcal control vaccine). In groups A-C, cases of shigellosis occurred 70-155 days after vaccination, whereas in group D cases occurred after 1-17 days. In groups A-C, the attack rate of shigellosis was 2.2% in recipients of S sonnei-rEPA compared with 8.6% in controls (protective efficacy 74% [95% CI 28-100], p = 0.006). S sonnei-rEPA also showed significant protection against shigellosis in group D (43% [4-82], p = 0.039). Prevaccination and postvaccination ELISA measurements of antibody to S sonnei lipopolysaccharide among recipients of S sonnei-rEPA showed that the vaccinees who developed S sonnei shigellosis had significantly lower serum IgG and IgA responses to the homologous lipopolysaccharide than those who did not (p = < 0.05). INTERPRETATION One injection of S sonnei-rEPA confers type-specific protection against S sonnei shigellosis. The high antibody concentration induced by the conjugate vaccine in volunteers who did not develop shigellosis suggests that there is an association between serum antibody titre and protection.

Correlation between Pertussis Toxin IgG Antibodies in Postvaccination Sera and Subsequent Protection against Pertussis

Both the protective antigen (PA) and the poly(γ-d-glutamic acid) capsule (γdPGA) are essential for the virulence of Bacillus anthracis. A critical level of vaccine-induced IgG anti-PA confers immunity to anthrax, but there is no information about the protective action of IgG anti-γdPGA. Because the number of spores presented by bioterrorists might be greater than encountered in nature, we sought to induce capsular antibodies to expand the immunity conferred by available anthrax vaccines. The nonimmunogenic γdPGA or corresponding synthetic peptides were bound to BSA, recombinant B. anthracis PA (rPA), or recombinant Pseudomonas aeruginosa exotoxin A (rEPA). To identify the optimal construct, conjugates of B. anthracis γdPGA, Bacillus pumilus γdLPGA, and peptides of varying lengths (5-, 10-, or 20-mers), of the d or l configuration with active groups at the N or C termini, were bound at 5–32 mol per protein. The conjugates were characterized by physico-chemical and immunological assays, including GLC-MS and matrix-assisted laser desorption ionization time-of-flight spectrometry, and immunogenicity in 5- to 6-week-old mice. IgG anti-γdPGA and antiprotein were measured by ELISA. The highest levels of IgG anti-γdPGA were elicited by decamers of γdPGA at 10 –20 mol per protein bound to the N- or C-terminal end. High IgG anti-γdPGA levels were elicited by two injections of 2.5 μg of γdPGA per mouse, whereas three injections were needed to achieve high levels of protein antibodies. rPA was the most effective carrier. Anti-γdPGA induced opsonophagocytic killing of B. anthracis tox–, cap+. γdPGA conjugates may enhance the protection conferred by PA alone. γdPGA-rPA conjugates induced both anti-PA and anti-γdPGA.

Development of an improved vaccine for anthrax

All acellular pertussis vaccines contain pertussis toxoid and induce protection against pertussis. This study investigated the relation between the postvaccination levels of pertussis toxin (PT) serum IgG and protection against pertussis. PT IgG was determined in sera obtained 21-77 days after the third vaccination from 813 children who received 3 doses of pertussis toxoid. The children were followed for 21-33 months after vaccination for the occurrence of pertussis. Of the children, 126 were exposed to pertussis in their households. The median PT IgG concentration was 79 U/mL in those who developed severe pertussis (>/=21 day of paroxysmal cough), 156 U/mL with mild pertussis (<21 days of paroxysmal cough), and 246 U/mL in those who did not develop pertussis (79 vs. 246, P<.0001). Corresponding values in the 687 children with no household exposure were 99, 124, and 155 U/mL, respectively (99 vs. 155, P<.0001). Thus, there is a highly significant correlation between the level of vaccine-induced serum PT IgG and protection against pertussis.