Manfred S. Green

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

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.

Reduction of transmission of shigellosis by control of houseflies (Musca domestica)

The effect of control of houseflies on the incidence of diarrhoea and shigellosis was evaluated in a prospective crossover intervention study at two military field bases several kilometers apart. In early summer, 1988, intensive fly control measures (mainly bait and trap strategy) were introduced on one base, while the other served as a control. After 11 weeks, as new cohorts arrived, the intervention was abruptly discontinued in the first base and instituted in the second for the next 11 weeks. The study was repeated the next summer. Overall, fly counts were 64% lower on the bases exposed to fly control measures (p = 0.024). Concomitantly, clinic visits dropped by 42% (p = 0.146) for diarrhoeal diseases and by 85% for shigellosis (p = 0.015), as did rates of seroconversion, by 76% (p = 0.024) for antibodies to Shigella and by 57% (p = 0.006) for antibodies to enterotoxigenic Escherichia coli. The findings indicate that houseflies, acting as mechanical vectors, transmit Shigella (and possibly enterotoxigenic E coli) diarrhoeal infections.

Age differences in immunity against wild and vaccine strains of poliovirus prior to the 1988 outbreak in Israel and response to booster immunization

During the 1988 type 1 polio outbreak in Israel, most cases occurred in previously vaccinated subjects aged 11-30 years, suggesting a possible age-related immunity deficit against the wild virus responsible for the outbreak. We examined type 1 poliovirus neutralizing antibody titres against the Sabin strain, the standard wild strain (Mahoney), the wild strain responsible for the 1988 outbreak and a previous wild strain from the region, on frozen sera drawn prior to the mass vaccination campaign from subjects aged 6 to 40 years. Response to vaccination with oral poliovaccine (OPV) was examined in a subgroup aged 18-40 years. At all ages, the highest antibody titres prior to the outbreak were against the Sabin strain. Geometric mean titres (GMTs) against both the Sabin strain and the wild Mahoney strain were significantly higher in the age groups 6-7, 12-13 and 30-40 years compared with the 18-29-year-olds. For the other wild strains, the GMT for those aged 30-40 years was significantly and substantially higher than in the other age groups, followed by the 12-13- and 6-7-year-olds and lowest in those aged 18-29 years. Following vaccination with OPV in subgroups aged 18-29 and 30-40 years, GMTs against Sabin and all wild strains were similar to each other and in both age groups. These findings suggest that there was a relative immunity gap against the wild type 1 strains in the age group that lacked prior exposure to wild virus and had received the last OPV dose more than 17 years previously.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term persistence of anti-diphtheria toxin antibodies among adults in Israel. Implications for vaccine policy.

Vaccination against diphtheria has essentially led to the disappearance of the disease in Israel. However, in other countries with high immunization coverage, isolated cases and small outbreaks have occurred in adults. Immunity following vaccination or natural exposure to toxigenic strains ofC. diphtheriae is conferred by serum antibodies to diphtheria toxin. Since booster doses of diphtheria toxoid are recommended every ten years in adults, this raises the question of persistence of protective levels Of anti-diphtheria toxin antibodies. In this study we assessed a possible age-related decline in anti-diphtheria toxin antibodies among adults in Israel. The study population comprised random samples in three age groups: 263 male recruits aged 18–19 years, 116 male reserve soldiers aged 25–35 years and 153 aged 41–51 years. Anti-diphtheria toxin antibody levels were measured by means of ELISA. Results indicate that 64.3% (95% CI=58.5–70.1%) of those aged 18–19 had anti-diphtheria toxin levels in excess of 0.1 IU ml−1, whereas the corresponding figures for ages 25–35 and 41–51 were 32.8% (95% CI=24.2–41.3%) and 15% (95% CI=9.4–20.7%). However, even in the oldest age group, 95.4% (95% CI=90.8–98.1%) had antibodies above the presumed protective level of 0.01 IU ml−1. Although these results indicate a significant age-related decline in anti-diphtheria toxin antibodies in vaccinated subjects, most had apparently protective levels. The absence of cases suggests that vaccine-induced immunity is long-lasting. However the immune status of the population should be carefully monitored.

Prevalence and correlates of diphtheria toxin antibodies among young adults in Israel

The paucity of information about immunity against diphtheria of young adults in Israel prompted us to analyse sera from a random sample of 480 recruits (263 males and 217 females) aged 18-19 years. Antitoxin antibody levels were determined by means of ELISA. Of the recruits 58.1% had antibody values greater than 0.1 IU/ml; 38.5% had amounts between 0.01 and 0.1 IU/ml, which is considered low when using the ELISA method, and 3.3% had less than 0.01 IU/ml. The results of this study suggest that a booster dose of antidiphtheria vaccine should be given to adults in Israel in order to ensure adequate antibody levels.

Efficacy of immune serum globulin in an outbreak of hepatitis A virus infection in adults

While immune serum globulin has been shown to be highly effective in preventing hepatitis A infection when administered before exposure to the virus, its efficacy when given after exposure is less clear. Timing of administration appears critical and the question of whether it modifies the clinical manifestations of the disease with possible asymptomatic seroconversion has not been conclusively answered. These aspects were examined in a common-source outbreak of 19 cases of hepatitis A in a military unit. Immune serum globulin administered between 2 and 3 weeks after suspected exposure to the virus did not modify clinical manifestations of the disease. Furthermore, in a subgroup studied serologically, there were eight clinical cases and only one case of asymptomatic seroconversion. Thus, late administration of immune serum globulin appears to have little effect on the clinical course of hepatitis A infection and does not appear to result in any significant degree of active-passive immunity.

Safety and immunogenicity of the oral E. coli K12-S. flexneri 2a vaccine (EcSf2a-2) among Israeli soldiers

A double-blind placebo-controlled study was carried out on the safety and immunogenicity of the oral Shigella flexneri (EcSf2a-2) vaccine among Israeli soldiers. Sixty volunteers received the vaccine and 59 received placebo. Fifty-three were given the full vaccine regimen (four doses). Doses ranged between 4.1 x 10(8) and 1.1 x 10(9) c.f.u. Visits to the unit clinic for mild gastrointestinal symptoms were common after the first dose in vaccinees (13%) as compared with placebo recipients (5%), but the difference was not significant, p = 0.12. Similarly, there was no difference between the groups for either gastrointestinal or non-gastrointestinal complaints reported by questionnaire. The vaccine strain was excreted by 69% and 67% of the vaccinees one day after receiving the second and the fourth doses, respectively. As judged by antibiotic susceptibility, phage typing and restriction fragment length polymorphism (RFLP), the vaccine strain emerged as genetically stable after replication in human gut and shedding. There was neither bacteriological nor serological evidence of transmission of the vaccine from vaccinees to placebo recipients. Eighteen of 26 (69.2%) and 11 of 30 (36.7%) vaccinees had significant IgA secreting cell responses 7 and 21 days after the first dose, respectively. Significant IgA or IgG serum antibody response to S. flexneri 2a LPS was detected in 30% of the vaccinees. These results support further evaluation of EcSf2a-2 vaccine protective efficacy in field studies.

Clinical Trials of Shigella Vaccines in Israel

Shigellosis or bacillary dysentery is caused by organisms belonging to genus Shigella, divided into four species (S. dysenteriae, S. boydii, S.flexneri and S. sonnei). With the exception of S. sonnei which has a single serotype, each species is divided into several serotypes according to the O-polysaccharide antigen of the cell wall (S. dysenteriae has 12 serotypes, S. flexneri has 6 serotypes, and S. boydii has 18 serotypes). Shigella spp. are invasive organisms that penetrate into the enterocytes of the colon epithelium, escape very quickly from the phagocytic vacuole and multiplicate intracellularly. Although non-motile, shigellae can move on an actin skeleton and spread to adjacent cells. The inflammatory process is usually limited to the lamina propria and does not involve the spread of Shigella deeper, into the submucosa. Pathogenesis in Shigella spp. is associated with a constellation of genes encoded on both the chromosome and a large 140 MDa virulence plasmid. These genes can be divided into two groups: regulatory genes and structural genes. The 140 MDa plasmid encodes for all the genes essential for invasion of Shigella into the epithelium of the colon. Regulatory genes are located on the virulence plasmid or on the chromosome.

Four-year follow-up of the immune status of young adults given a single booster dose of trivalent oral poliovaccine

In 1988 an outbreak of type 1 paralytic poliomyelitis occurred in Israel. Almost the entire population in the age group 0-40 years received a single dose of trivalent oral polio vaccine. We examined the serological responses to the vaccine at 2 weeks and 4 years later, in a group of 17 vaccines. Geometric mean antibody titres (GMTs) against both the type 1 epidemic and Mahoney strains had declined by about 50% from the levels found at 2 weeks after vaccination. However, they were still more than five times higher than the prevaccination levels. All vaccines had neutralizing antibody titres against both the type 1 strains of at least 1:64, well above the 1:8 titre regarded as protective. The GMTs against the type 2 and 3 strains declined to about one-third of the 2-week postvaccination levels but were also well above protective levels. These findings indicate that antibody titres against both the Mahoney and epidemic type 1 strains remained at very adequate levels over a period of at least 4 years. Thus the immunity resulting from a single booster dose of oral poliovaccine in young adults is likely to be long-lasting, a finding of particular importance for travellers on extended visits to endemic areas.

Mumps vaccination of young adults is unwarranted

A clinical and epidemiological study of mumps was carried out over a 18-month period and included 104 soldiers (61% of the reported cases in the Israel Defence Forces). The average number of days off work was 12.9 +/- 9.2 days. The most common complication was orchitis (19/72 men; 26%), followed by 3 cases of pancreatitis (3%) and 2 cases of meningitis (2%). 13 men with orchitis were tested, and all had normal spermograms. No long term important sequelae were described. The transmission rate was low with no respondent reporting more than one secondary case among soldiers serving in the same unit. The socio-economic level of mumps patients was comparable to that of the general army population at the time of the study. Our data do not support a mass immunization program of the adult population.