Stanley J. Cryz

SAFETY, IMMUNOGENICITY, AND EFFICACY OF RECOMBINANT LIVE ORAL CHOLERA VACCINES, CVD 103 AND CVD 103-HgR

The genes encoding the A (toxic) subunit of cholera toxin were deleted from pathogenic Vibrio cholerae O1 strain 569B by recombinant techniques, leaving intact production of immunogenic, non-toxic B subunit. The resultant strain, CVD 103, evaluated for safety, immunogenicity, and efficacy as a live oral vaccine, was highly attenuated and elicited strong antibacterial and antitoxic immune responses; a single dose significantly protected volunteers against challenge with pathogenic V cholerae O1 of either serotype or biotype. A further derivative, CVD 103-HgR, which has an Hg++-resistance gene to differentiate it from wild-type vibrios, was also well-tolerated, immunogenic, and protective; moreover, faecal excretion of this derivative was significantly lower than that of CVD 103, which should minimise environmental spread of the vaccine. CVD 103-HgR is a candidate for expanded clinical trials in endemic areas.

Efficacy trial of single-dose live oral cholera vaccine CVD 103-HgR in North Jakarta, Indonesia, a cholera-endemic area

A randomized, double-blind, placebo-controlled efficacy trial of one dose of CVD 103-HgR live oral cholera vaccine was performed in Indonesia from 1993 to 1997. 67,508 persons aged 2-41 years ingested vaccine or placebo and were followed for four years, detecting cholera cases using hospital-based surveillance. A nested reactogenicity study (538 vaccinees, 535 controls) revealed no vaccine-attributable side effects. A nested immunogenicity study (N=657) showed vibriocidal seroresponses in 64-70% of vaccinees vs 1-2% of controls. Cholera incidence was lower than expected. 103 cases of Vibrio cholerae O1 El Tor diarrhea were detected, 93 evaluable for vaccine efficacy (43 vaccine, 50 placebo; efficacy=14%). A suggestion of protection was observed among persons with blood group O [P=0.12]. Only seven cases occurred within six months of vaccination, precluding assessment of short-term efficacy. In Jakarta, single-dose CVD 103-HgR did not confer long-term protection. Short-term protection from a single-dose and long-term protection from two doses have yet to be studied.

Immunogenicity of new virosome influenza vaccine in elderly people

The safety and immunogenicity of a new virosome influenza vaccine was compared to commercial whole-virus vaccine and subunit vaccine in elderly people. The virosome vaccine was made by extracting the haemagglutinin from influenza virus and incorporating it into the membrane of liposomes composed of phosphatidylcholine (PC) and phosphatidylethanolamine (PE). 126 residents of a nursing home, aged 63-102, were randomised to receive one of the vaccines. All three were well tolerated and caused a significant rise in the geometric mean anti-haemagglutinin inhibiting (HAI) antibody titre to the 3 vaccine components (H1N1 Singapore, H3N2 Beijing, and B/Yamagata). The virosome formulation caused the highest geometric mean titres in addition to significantly (p = 0.039-0.0016) higher rates of more than four-fold or more titre rises to all 3 vaccine components. The percentage of those immunised who achieved protective levels of antibody (HAI > or = 40) was significantly (p = 0.035-0.0017) higher for the H1N1 and B/Yamagata strains following immunisation with virosome formulation. Participants with non-protective baseline titres to the H1N1 or B/Yamagata strains were more likely (p = 0.0049-0.006) to achieve protective levels of antibodies after immunisation with the virosome vaccine. Immunisation with the virosome formulation did not result in a significant rise in anti-PC or anti-PE antibodies.

Duration of efficacy of Ty21a, attenuated Salmonella typhi live oral vaccine.

Currently, two different formulations of Ty21a live oral typhoid vaccine are commercialized. The enteric-coated capsule formulation was licensed based on results of three years of follow-up of a randomized, placebo-controlled, double-blind field trial in Area Occidente, Santiago, Chile, which demonstrated that three doses of this formulation, given on an every other day immunization schedule, conferred the best protection among several options evaluated. Subsequently, a liquid formulation (lyophilized vaccine organisms reconstituted with buffer and water into a vaccine cocktail) was commercialized after it was shown to provide superior protection than enteric-coated capsules over three years of follow-up in a randomized, placebo-controlled field trial in Area Sur Oriente and Area Norte, Santiago. Surveillance in the Area Occidente trial was continued for four additional years (i.e., total seven years of follow-up) and in the Area Sur Oriente/Area Norte trial for two additional years (i.e., a total of five years of follow-up). These additional surveillance data, which were analyzed to ascertain the longevity of protection conferred by these formulations of Ty21a, revealed that three doses of Ty21a in enteric-coated capsules (every other day schedule) conferred 67% protection over three years and 62% protection over seven years of follow-up, whereas three doses of liquid formulation (every other day schedule) elicited 77% protection over three years and 78% over five years of follow-up. Based on its excellent clinical acceptability, ease of oral administration, proven practicality in school-based mass immunization, and long-term efficacy enduring at least seven years, it is proposed that school-based immunization with Ty21a be utilized as a control measure in areas where the incidence of typhoid fever is high and Salmonella typhi are antibiotic-resistant.

Comparison of enteric-coated capsules and liquid formulation of Ty21a typhoid vaccine in randomised controlled field trial

In a randomised, double-blind, controlled field trial in Santiago, Chile, 81,621 schoolchildren aged 5-19 years received three doses, within a week, of attenuated Salmonella typhi oral vaccine Ty21a in enteric-coated capsules or in a new liquid suspension, or placebo. Over 36 months of surveillance, the liquid formulation (76.9% vaccine efficacy) was significantly superior to the enteric-coated capsules (33.2% vaccine efficacy). The liquid formulation protected young children (5-9 years) (efficacy 82.3%) as well as older children (efficacy 69.3%), whereas the capsules significantly protected only older children. The liquid suspension was easy to prepare by mixing lyophilised vaccine with buffer in water and was easily administered, even to the youngest children. Thus, the liquid formulation of Ty21a is preferable to enteric-coated capsules.

Safety and immunogenicity of single-dose live oral cholera vaccine CVD 103-HgR in 5-9-year-old Indonesian children.

Oral vaccines offer great promise as public-health measures to prevent disease in less-developed countries. CVD 103-HgR, a genetically engineered, attenuated, Vibrio cholerae O1 strain has proved effective in industrialised countries. We have assessed the safety, immunogenicity, and excretion of this live cholera vaccine in children in north Jakarta, Indonesia. 412 children aged 5-9 years received single doses of 5 x 10(6), 5 x 10(7), 5 x 10(8), 5 x 10(9), or 1 x 10(10) colony forming units (CFU) of CVD 103-HgR or placebo (5 x 10(8) inactivated Escherichia coli K-12) with buffer. All doses were well tolerated. The 5 x 10(8) CFU dose, which is highly immunogenic in subjects in industrialised countries (greater than 90% seroconversion), elicited seroconversions of vibriocidal antibody in only 16% of Indonesian children. By contrast, a single 5 x 10(9) CFU dose of vaccine resulted in high rates (75% and 87%) of seroconversion with two different batches of vaccine. A batch prepared with a centrifugation step gave significantly higher geometric mean titres (16-fold increase over baseline) than did a batch in which there was a filtration step between fermentation and lyophilisation (10-fold increase over baseline). At a 5 x 10(9) CFU dose, CVD 103-HgR is well tolerated and highly immunogenic in Indonesian children and should therefore be further investigated for use as a one-dose live oral cholera vaccine in developing countries.

Studies in volunteers to evaluate candidate Shigella vaccines: further experience with a bivalent Salmonella typhi-Shigella sonnei vaccine and protection conferred by previous Shigella sonnei disease

A bivalent vaccine consisting of Salmonella typhi strain Ty21a containing the 120 MDa plasmid of Shigella sonnei and expressing both S. typhi and S. sonnei lipopolysaccharides (LPS) on its surface was previously shown to protect significantly against S. sonnei disease in experimental challenge studies. However, protective efficacy could not be reconfirmed in volunteers with five subsequent lots of vaccine. One vaccine lot which resembled the initial protective lots of vaccine in biochemical and serological tests, and by electron microscopy, was administered to 16 volunteers who ingested three doses of 10(9) organisms each. Antibody secreting cells (ASC) specific for S. sonnei LPS were detected in the blood of 100% of vaccines, but no protection of these vaccines was demonstrated during a S. sonnei challenge study. To assess the ability of the volunteer model to detect infection-derived immunity, six volunteers who had had clinical shigellosis due to S. sonnei two months earlier were rechallenged with wild-type S. sonnei, together with 12 controls. Prior infection provided 100% protection against febrile illness (p = 0.05) and diarrhea (p = 0.04), thereby validating the volunteer model for assessing Shigella vaccines.

Immunogenicity of trivalent subunit versus virosome-formulated influenza vaccines in geriatric patients.

The safety and immunogenicity of a commercial trivalent subunit influenza vaccine and an experimental virosome-formulated influenza vaccine were evaluated among geriatric patients in a double-blind, randomized manner. The virosome vaccine was produced by incorporating hemagglutinin (HA) into the membrane of liposomes composed of phosphatidylcholine. Both vaccines elicited a significant (P < 0.01) rise in the geometric mean anti-HA antibody titer to all three vaccine components 1 month after immunization. However, significantly (P < 0.005) more subjects vaccinated with the virosome preparation mounted a more than fourfold rise to the A/Singapore and A/Beijing strains compared with those who received subunit vaccine. The percentage of patients who attained protective levels (anti-HA titer > or = 40) of anti-A/Beijing antibody was also significantly (P < 0.005) higher in the virosome group. Subjects who possessed non-protective baseline antibody levels to the A/Singapore and A/Beijing strains were more likely (P < 0.005-0.030) to achieve protective levels after immunization with the virosome vaccine than with the subunit vaccine. Of particular clinical significance was the fact that 68.4% of subjects immunized with the virosome vaccine attained protective levels of antibody to all three vaccine components versus 38% for the subunit vaccine (P = 0.010).

Safety and immunogenicity of intranasally administered inactivated trivalent virosome-formulated influenza vaccine containing Escherichia coli heat-labile toxin as a mucosal adjuvant.

A trivalent influenza virosome vaccine containing hemagglutinin and Escherichia coli heat-labile toxin (HLT) was administered intranasally to young adults and elderly subjects. Symptoms that followed immunization were mild and transient. A significant increase in serum hemagglutination inhibition (HI) antibody was noted for the 3 vaccine strains. There was no significant difference in postimmunization geometric mean titers or seroconversion rates between age groups. The percentage of subjects attaining protective HI titers (>/=40%) was comparable in both groups for the A/Bayern (P=.5) and B/Beijing (P=.3) strains but was higher among young adults (92.2%) versus elderly subjects (76.5%; P=.057) for the A/Wuhan strain. The proportion of subjects with nonprotective baseline titers who attained protective levels after immunization was similar in both age groups for the A/Bayern and B/Beijing components. For the A/Wuhan component, significantly (P=.017) more young adults achieved protective titers versus elderly subjects (85. 7% and 53.8%, respectively). Vaccination evoked a significant (P<. 005) increase in anti-HLT antibody titers.

Safety and immunogenicity of Pseudomonas aeruginosa conjugate A vaccine in cystic fibrosis

To assess the safety and immunogenicity of a Pseudomonas aeruginosa octavalent O-polysaccharide-toxin A conjugate vaccine, 22 patients (mean age 7 years) with cystic fibrosis who had no history of colonisation with P aeruginosa were immunised with the vaccine. Adverse reactions were mild and self-limiting. IgG antibody concentrations to all vaccine antigens were significantly raised after vaccination and remained so for 12 months. Immunisation produced opsonic and toxin A neutralising antibodies. A booster dose given at 12 months led to an anamnestic response. There was no significant change in clinical status after vaccination. Further work to assess efficacy in patients with cystic fibrosis can now be considered since our findings support the safety and immunogenicity of the vaccine.